Display Scheduler: Don't request BeginFrames while waiting for a root surface

When the root surface changes, we cannot draw to the display until a surface
activates. This CL stops draws (and BeginFrames) until activation. If a root surface is never
submitted then the display will not listen for BeginFrames.

Bug: 821940
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I749c0ca8e85a3dbc7eccaa0799add81afb15beb9
Reviewed-on: https://chromium-review.googlesource.com/964595Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543548}

components/viz/service/display/display_scheduler.cc

@@ -70,7 +70,11 @@ void DisplayScheduler::SetVisible(bool visible) {
 void DisplayScheduler::SetRootSurfaceResourcesLocked(bool locked) {
   TRACE_EVENT1("viz", "DisplayScheduler::SetRootSurfaceResourcesLocked",
                "locked", locked);
+  if (root_surface_resources_locked_ == locked)
+    return;
+
   root_surface_resources_locked_ = locked;
+  MaybeStartObservingBeginFrames();
   ScheduleBeginFrameDeadline();
 }
 
@@ -292,7 +296,8 @@ void DisplayScheduler::StopObservingBeginFrames() {
 bool DisplayScheduler::ShouldDraw() {
   // Note: When any of these cases becomes true, MaybeStartObservingBeginFrames
   // must be called to ensure the draw will happen.
-  return needs_draw_ && !output_surface_lost_ && visible_;
+  return needs_draw_ && !output_surface_lost_ && visible_ &&
+         !root_surface_resources_locked_;
 }
 
 void DisplayScheduler::OnBeginFrameSourcePausedChanged(bool paused) {
@@ -478,7 +483,7 @@ bool DisplayScheduler::AttemptDrawAndSwap() {
   begin_frame_deadline_task_time_ = base::TimeTicks();
 
   if (ShouldDraw()) {
-    if (pending_swaps_ < max_pending_swaps_ && !root_surface_resources_locked_)
+    if (pending_swaps_ < max_pending_swaps_)
       return DrawAndSwap();
   } else {
     // We are going idle, so reset expectations.

components/viz/service/display/display_scheduler_unittest.cc

@@ -629,10 +629,14 @@ TEST_F(DisplaySchedulerTest, RootSurfaceResourcesLocked) {
 
   //  Deadline triggers normally when root resources are unlocked.
   AdvanceTimeAndBeginFrameForTest({sid1, root_surface_id});
-  late_deadline = now_src().NowTicks() + BeginFrameArgs::DefaultInterval();
+  EXPECT_FALSE(scheduler_.inside_begin_frame_deadline_interval());
   SurfaceDamaged(sid1);
+
+  // The deadline is not updated because the display scheduler does not receive
+  // a BeginFrame while root resources are locked.
   EXPECT_EQ(late_deadline, scheduler_.DesiredBeginFrameDeadlineTimeForTest());
   scheduler_.SetRootSurfaceResourcesLocked(false);
+  EXPECT_TRUE(scheduler_.inside_begin_frame_deadline_interval());
   SurfaceDamaged(root_surface_id);
   EXPECT_EQ(base::TimeTicks(),
             scheduler_.DesiredBeginFrameDeadlineTimeForTest());