Work on issue #17357238: Recents is often slow if not used in a while

Add a new activity attribute, resumeWhilePausing, that allows an
activity specifying it to immediately start running without waiting
for the previous activity to pause.  The recents activity is updated
to use this.

The implementation of this is ultimately fairly simple -- if we are
in the path of resuming such an activity, and find that we first need
to pause the existing activity, then within the activity manager we
do the regular pause flow but act like it has immediately finished
pausing right then so that we can immediately go on to the resume.
To make this clean, we tell the activity when asking it to pause that
it should not come back and tell us it is done, because we aren't in
any way waiting for it.

One potentially important change I needed to make here is the pause
callback no longer provides the saved persistent state, because we
now can't count on that callback happening.  I don't think there was
really any utility in this anyway -- all modern apps will have their
save state flow happen as part of stopping, not pausing, so we'll
only capture that saved state when the stop is reported back anyway.
And since we do send the saved state back when stopping, it would
always blow away whatever we had gotten at the pause.

Finally, update the documentation for AppTask.startActivity(), and
fix the implementation handling that to be cleaner -- we need to
deal with inTask first before getting in to "oh noes add NEW_TASK
if this isn't coming from a calling activity" flow.

Change-Id: Ia1da0fac90d7bdbaafdda2e34850d795ce17a39f

2 files changed, 12 insertions, 2 deletions

diff --git a/core/res/res/values/attrs_manifest.xml b/core/res/res/values/attrs_manifest.xml
index e905a3a..10c2518 100644
--- a/core/res/res/values/attrs_manifest.xml
+++ b/core/res/res/values/attrs_manifest.xml
@@ -939,7 +939,7 @@
          {@link android.content.Intent#FLAG_ACTIVITY_MULTIPLE_TASK
          Intent.FLAG_ACTIVITY_MULTIPLE_TASK}. If the value of
          documentLaunchModes is <code>never</code> then any use of
-.........{@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT
+         {@link android.content.Intent#FLAG_ACTIVITY_NEW_DOCUMENT
          Intent.FLAG_ACTIVITY_NEW_DOCUMENT} to launch this activity will be ignored. -->
     <attr name="documentLaunchMode">
         <!-- The default mode, which will create a new task only when
@@ -994,6 +994,15 @@
          TaskDescription to change labels, colors and icons in the recent task list. -->
     <attr name="relinquishTaskIdentity" format="boolean" />
 
+    <!-- Indicate that it is okay for this activity be resumed while the previous
+         activity is in the process of pausing, without waiting for the previous pause
+         to complete.  Use this with caution: your activity can not acquire any exclusive
+         resources (such as opening the camera or recording audio) when it launches, or it
+         may conflict with the previous activity and fail.
+
+         <p>The default value of this attribute is <code>false</code>. -->
+    <attr name="resumeWhilePausing" format="boolean" />
+
     <!-- The <code>manifest</code> tag is the root of an
          <code>AndroidManifest.xml</code> file,
          describing the contents of an Android package (.apk) file.  One
@@ -1678,6 +1687,7 @@
         <attr name="maxRecents" />
         <attr name="autoRemoveFromRecents" />
         <attr name="relinquishTaskIdentity" />
+        <attr name="resumeWhilePausing" />
     </declare-styleable>
     
     <!-- The <code>activity-alias</code> tag declares a new
diff --git a/core/res/res/values/public.xml b/core/res/res/values/public.xml
index a4c3474..5b047f7 100644
--- a/core/res/res/values/public.xml
+++ b/core/res/res/values/public.xml
@@ -2266,7 +2266,7 @@
   <public type="attr" name="windowReenterTransition" />
   <public type="attr" name="windowSharedElementReturnTransition" />
   <public type="attr" name="windowSharedElementReenterTransition" />
-  <public type="attr" name="__removed1" />
+  <public type="attr" name="resumeWhilePausing" />
   <public type="attr" name="datePickerMode"/>
   <public type="attr" name="timePickerMode"/>
   <public type="attr" name="inset" />