Reduce wasted buffer allocations

Bug: 20170924

Don't pre-allocate buffers if there is a SurfaceView or other
View that has requested transparent regions. This doesn't fully
address the problem of allocating buffers when there's a full
screen SurfaceView but it at least gets back to KitKat levels
of only having 1 wasted buffer instead of 3 (the 1 being
a result of the fact that it will still draw one frame of emptiness
forcing a buffer dequeue).

Change-Id: Ied9553186bc7b111d180b63f87b92bd317cb4b97

core/java/android/view/ThreadedRenderer.java

@@ -148,7 +148,6 @@ public class ThreadedRenderer extends HardwareRenderer {
         mInitialized = true;
         updateEnabledState(surface);
         boolean status = nInitialize(mNativeProxy, surface);
-        surface.allocateBuffers();
         return status;
     }
 

core/java/android/view/ViewRootImpl.java

@@ -1708,10 +1708,19 @@ public final class ViewRootImpl implements ViewParent,
                         mFullRedrawNeeded = true;
                         mPreviousTransparentRegion.setEmpty();
 
+                        // Only initialize up-front if transparent regions are not
+                        // requested, otherwise defer to see if the entire window
+                        // will be transparent
                         if (mAttachInfo.mHardwareRenderer != null) {
                             try {
                                 hwInitialized = mAttachInfo.mHardwareRenderer.initialize(
                                         mSurface);
+                                if (hwInitialized && (host.mPrivateFlags
+                                        & View.PFLAG_REQUEST_TRANSPARENT_REGIONS) == 0) {
+                                    // Don't pre-allocate if transparent regions
+                                    // are requested as they may not be needed
+                                    mSurface.allocateBuffers();
+                                }
                             } catch (OutOfResourcesException e) {
                                 handleOutOfResourcesException(e);
                                 return;