[animation-worklet] Fix crash in tests when running on main thread

Worklet animation supports invalidation of its compositing state.

This patch makes this invalidation process a no-op for animations that are
running on main (i.e., |compositor_animation_| is null). This means we no longer
try to read/modify the non-existent |compositor_animation_| which was causing
the crash.

Note that in some situations, even for currently main thread animaiton, we may
actually want to create and start the |compositor_animation_| but this is a
separate issue that can be fixed as a follow up.

The added DCHECK uncovered a bug where we were attaching the worklet animation
to early even if play was failing. This is also fixed.

Bug: 887659, 889330
Change-Id: I4a89de6632e053f68beafb810355c25e4bfba0e3
Reviewed-on: https://chromium-review.googlesource.com/c/1249387
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597199}

third_party/WebKit/LayoutTests/TestExpectations

@@ -5236,13 +5236,9 @@ crbug.com/887659 animations/animationworklet/animation-worklet-inside-iframe.htm
 crbug.com/887659 animations/animationworklet/animator-animate.html [ Failure ]
 crbug.com/887659 animations/animationworklet/animator-with-options.html [ Failure ]
 crbug.com/887659 animations/animationworklet/peek-updated-composited-property-on-main.html [ Failure ]
-crbug.com/887659 animations/animationworklet/scroll-timeline-display-none.html [ Crash ]
-crbug.com/887659 animations/animationworklet/scroll-timeline-dynamic-update.html [ Crash ]
 crbug.com/887659 animations/animationworklet/worklet-animation-currentTime.html [ Failure ]
 crbug.com/887659 animations/animationworklet/worklet-animation-local-time-after-duration.html [ Failure ]
 crbug.com/887659 animations/animationworklet/worklet-animation-local-time-undefined.html [ Failure ]
-crbug.com/887659 animations/animationworklet/worklet-animation-set-keyframes.html [ Crash ]
-crbug.com/887659 animations/animationworklet/worklet-animation-set-timing.html [ Crash ]
 crbug.com/887659 animations/animationworklet/worklet-animation-style-update.html [ Failure ]
 crbug.com/887659 animations/animationworklet/worklet-animation-responsive-to-zoom.html [ Crash ]
 

third_party/blink/renderer/modules/animationworklet/worklet_animation.cc

@@ -306,7 +306,6 @@ void WorkletAnimation::play(ExceptionState& exception_state) {
   DCHECK(IsMainThread());
   if (play_state_ == Animation::kPending)
     return;
-  document_->GetWorkletAnimationController().AttachAnimation(*this);
 
   String failure_message;
   if (!CheckCanStart(&failure_message)) {
@@ -315,6 +314,7 @@ void WorkletAnimation::play(ExceptionState& exception_state) {
     return;
   }
 
+  document_->GetWorkletAnimationController().AttachAnimation(*this);
   SetPlayState(Animation::kPending);
 
   for (auto& effect : effects_) {
@@ -416,6 +416,8 @@ void WorkletAnimation::SetStartTimeToNow() {
 }
 
 void WorkletAnimation::UpdateCompositingState() {
+  DCHECK(play_state_ != Animation::kIdle && play_state_ != Animation::kUnset);
+
   if (play_state_ == Animation::kPending) {
     String warning_message;
     DCHECK(CheckCanStart(&warning_message));
@@ -429,8 +431,14 @@ void WorkletAnimation::UpdateCompositingState() {
         kOtherMessageSource, kWarningMessageLevel, message));
     StartOnMain();
   } else if (play_state_ == Animation::kRunning) {
-    UpdateOnCompositor();
+    // TODO(majidvp): If keyframes have changed then it may be possible to now
+    // run the animation on compositor. The current logic does not allow this
+    // switch from main to compositor to happen.
+    if (!running_on_main_thread_)
+      UpdateOnCompositor();
   }
+  DCHECK(running_on_main_thread_ != !!compositor_animation_)
+      << "Active worklet animation should either run on main or compositor";
 }
 
 void WorkletAnimation::InvalidateCompositingState() {