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diff --git a/Source/WebCore/dom/CanvasSurface.cpp b/Source/WebCore/dom/CanvasSurface.cpp
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+/*
+ * Copyright (C) 2010 Google Inc. All rights reserved.
+ * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "CanvasSurface.h"
+
+#include "AffineTransform.h"
+#include "ExceptionCode.h"
+#include "FloatRect.h"
+#include "GraphicsContext.h"
+#include "HTMLCanvasElement.h"
+#include "ImageBuffer.h"
+#include "MIMETypeRegistry.h"
+
+namespace WebCore {
+
+// These values come from the WhatWG spec.
+const int CanvasSurface::DefaultWidth = 300;
+const int CanvasSurface::DefaultHeight = 150;
+
+// Firefox limits width/height to 32767 pixels, but slows down dramatically before it
+// reaches that limit. We limit by area instead, giving us larger maximum dimensions,
+// in exchange for a smaller maximum canvas size.
+const float CanvasSurface::MaxCanvasArea = 32768 * 8192; // Maximum canvas area in CSS pixels
+
+CanvasSurface::CanvasSurface(float pageScaleFactor)
+    : m_size(DefaultWidth, DefaultHeight)
+#if PLATFORM(ANDROID)
+    /* In Android we capture the drawing into a displayList, and then replay
+     * that list at various scale factors (sometimes zoomed out, other times
+     * zoomed in for "normal" reading, yet other times at arbitrary zoom values
+     * based on the user's choice). In all of these cases, we do not re-record
+     * the displayList, hence it is usually harmful to perform any pre-rounding,
+     * since we just don't know the actual drawing resolution at record time.
+     */
+    // TODO - may be better to move the ifdef to the call site of this
+    // constructor
+    , m_pageScaleFactor(1.0f)
+#else
+    , m_pageScaleFactor(pageScaleFactor)
+#endif
+    , m_originClean(true)
+    , m_hasCreatedImageBuffer(false)
+{
+}
+
+CanvasSurface::~CanvasSurface()
+{
+}
+
+void CanvasSurface::setSurfaceSize(const IntSize& size)
+{
+    m_size = size;
+    m_hasCreatedImageBuffer = false;
+    m_imageBuffer.clear();
+}
+
+String CanvasSurface::toDataURL(const String& mimeType, const double* quality, ExceptionCode& ec)
+{
+    if (!m_originClean) {
+        ec = SECURITY_ERR;
+        return String();
+    }
+
+    if (m_size.isEmpty() || !buffer())
+        return String("data:,");
+
+    String lowercaseMimeType = mimeType.lower();
+
+    // FIXME: Make isSupportedImageMIMETypeForEncoding threadsafe (to allow this method to be used on a worker thread).
+    if (mimeType.isNull() || !MIMETypeRegistry::isSupportedImageMIMETypeForEncoding(lowercaseMimeType))
+        return buffer()->toDataURL("image/png");
+
+    return buffer()->toDataURL(lowercaseMimeType, quality);
+}
+
+void CanvasSurface::willDraw(const FloatRect&)
+{
+    if (m_imageBuffer)
+        m_imageBuffer->clearImage();
+}
+
+IntRect CanvasSurface::convertLogicalToDevice(const FloatRect& logicalRect) const
+{
+    return IntRect(convertLogicalToDevice(logicalRect.location()), convertLogicalToDevice(logicalRect.size()));
+}
+
+IntSize CanvasSurface::convertLogicalToDevice(const FloatSize& logicalSize) const
+{
+    float wf = ceilf(logicalSize.width() * m_pageScaleFactor);
+    float hf = ceilf(logicalSize.height() * m_pageScaleFactor);
+
+    if (!(wf >= 1 && hf >= 1 && wf * hf <= MaxCanvasArea))
+        return IntSize();
+
+    return IntSize(static_cast<unsigned>(wf), static_cast<unsigned>(hf));
+}
+
+IntPoint CanvasSurface::convertLogicalToDevice(const FloatPoint& logicalPos) const
+{
+    float xf = logicalPos.x() * m_pageScaleFactor;
+    float yf = logicalPos.y() * m_pageScaleFactor;
+
+    return IntPoint(static_cast<unsigned>(xf), static_cast<unsigned>(yf));
+}
+
+void CanvasSurface::createImageBuffer() const
+{
+    ASSERT(!m_imageBuffer);
+
+    m_hasCreatedImageBuffer = true;
+
+    FloatSize unscaledSize(width(), height());
+    IntSize size = convertLogicalToDevice(unscaledSize);
+    if (!size.width() || !size.height())
+        return;
+
+    m_imageBuffer = ImageBuffer::create(size);
+    // The convertLogicalToDevice MaxCanvasArea check should prevent common cases
+    // where ImageBuffer::create() returns 0, however we could still be low on memory.
+    if (!m_imageBuffer)
+        return;
+    m_imageBuffer->context()->scale(FloatSize(size.width() / unscaledSize.width(), size.height() / unscaledSize.height()));
+    m_imageBuffer->context()->setShadowsIgnoreTransforms(true);
+}
+
+GraphicsContext* CanvasSurface::drawingContext() const
+{
+    return buffer() ? m_imageBuffer->context() : 0;
+}
+
+ImageBuffer* CanvasSurface::buffer() const
+{
+    if (!m_hasCreatedImageBuffer)
+        createImageBuffer();
+    return m_imageBuffer.get();
+}
+
+AffineTransform CanvasSurface::baseTransform() const
+{
+    ASSERT(m_hasCreatedImageBuffer);
+    FloatSize unscaledSize(width(), height());
+    IntSize size = convertLogicalToDevice(unscaledSize);
+    AffineTransform transform;
+    if (size.width() && size.height())
+        transform.scaleNonUniform(size.width() / unscaledSize.width(), size.height() / unscaledSize.height());
+    transform.multiply(m_imageBuffer->baseTransform());
+    return transform;
+}
+
+// FIXME: Everything below here relies on CanvasSurface really being
+// a HTMLCanvasElement.
+const SecurityOrigin& CanvasSurface::securityOrigin() const
+{
+    return *(static_cast<const HTMLCanvasElement*>(this)->document()->securityOrigin());
+}
+
+RenderBox* CanvasSurface::renderBox() const
+{
+    return static_cast<const HTMLCanvasElement*>(this)->renderBox();
+}
+
+RenderStyle* CanvasSurface::computedStyle()
+{
+    return static_cast<HTMLCanvasElement*>(this)->computedStyle();
+}
+
+CSSStyleSelector* CanvasSurface::styleSelector()
+{
+    return static_cast<HTMLCanvasElement*>(this)->document()->styleSelector();
+}
+
+} // namespace WebCore