BLASTBufferQueue: Fix two conditions leading to freeze.

If we ask the BLASTBufferQueue to redirect a buffer in to a transaction
but then lose the buffer the app will of course eventually ANR as it
is stuck on EGLSwapBuffers. Here we fix two cases where this could have
happened:
	1. Currently if we are blast syncing and report draw is true
	we send the buffer to the WM. This is from an earlier version of
	the code and is not correct. The WM now explicitly notifies us
	if it wants to receive the buffer, and so we avoid sending it if
	it hasn't asked.
	2. We should pause the renderer in addition to fencing it
	otherwise a render thread animation frame could sneak in. We are
	right on the verge of kicking off a new frame so this shouldn't
	have much impact besides ensuring overlapping frames don't
	confuse our transaction logic.

Bug: 155300507
Test: Existing tests pass.
Change-Id: I816d806da6c09ae12734de8909c0e61af433f93f

core/java/android/view/ViewRootImpl.java

@@ -704,6 +704,11 @@ public final class ViewRootImpl implements ViewParent,
     // draw returns.
     private SurfaceControl.Transaction mRtBLASTSyncTransaction = new SurfaceControl.Transaction();
 
+    // Keeps track of whether the WM requested us to use BLAST Sync when calling relayout.
+    //  We use this to make sure we don't send the WM transactions from an internal BLAST sync
+    // (e.g. SurfaceView)
+    private boolean mSendNextFrameToWm = false;
+
     private HashSet<ScrollCaptureCallback> mRootScrollCaptureCallbacks;
 
     private String mTag = TAG;
@@ -3053,6 +3058,7 @@ public final class ViewRootImpl implements ViewParent,
         if ((relayoutResult & WindowManagerGlobal.RELAYOUT_RES_BLAST_SYNC) != 0) {
             reportNextDraw();
             setUseBLASTSyncTransaction();
+            mSendNextFrameToWm = true;
         }
 
         boolean cancelDraw = mAttachInfo.mTreeObserver.dispatchOnPreDraw() || !isViewVisible;
@@ -3762,7 +3768,7 @@ public final class ViewRootImpl implements ViewParent,
             if (needFrameCompleteCallback) {
                 final Handler handler = mAttachInfo.mHandler;
                 mAttachInfo.mThreadedRenderer.setFrameCompleteCallback((long frameNr) -> {
-                        finishBLASTSync(!reportNextDraw);
+                        finishBLASTSync(!mSendNextFrameToWm);
                         handler.postAtFrontOfQueue(() -> {
                             if (reportNextDraw) {
                                 // TODO: Use the frame number
@@ -3784,7 +3790,7 @@ public final class ViewRootImpl implements ViewParent,
                 // so if we are BLAST syncing we make sure the previous draw has
                 // totally finished.
                 if (mAttachInfo.mThreadedRenderer != null) {
-                    mAttachInfo.mThreadedRenderer.fence();
+                    mAttachInfo.mThreadedRenderer.pause();
                 }
 
                 mNextReportConsumeBLAST = true;
@@ -9752,6 +9758,7 @@ public final class ViewRootImpl implements ViewParent,
     }
 
     private void finishBLASTSync(boolean apply) {
+        mSendNextFrameToWm = false;
         if (mNextReportConsumeBLAST) {
             mNextReportConsumeBLAST = false;