Lazily Obtain the Compositor

If we set |compositor_| during AddedToWidget() and not call Play(), the
compositor could shutdown and we would never clear |compositor_| since
we're not registered as an AnimationObserver and will miss
OnCompositingShuttingDown().

BUG=899112

Change-Id: If1dbe4ae9db80d55d3d5db6d939da6008bf97160
Reviewed-on: https://chromium-review.googlesource.com/c/1300694
Commit-Queue: Robert Liao <robliao@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Malay Keshav <malaykeshav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603253}

ui/views/controls/animated_image_view.cc

@@ -52,13 +52,7 @@ void AnimatedImageView::Play() {
 
   state_ = State::kPlaying;
 
-  // We cannot play the animation unless we have a valid compositor.
-  if (!compositor_)
-    return;
-
-  // Ensure the class is added as an observer to receive clock ticks.
-  if (!compositor_->HasAnimationObserver(this))
-    compositor_->AddAnimationObserver(this);
+  SetCompositorFromWidget();
 
   animated_image_->Start();
 }
@@ -68,8 +62,7 @@ void AnimatedImageView::Stop() {
     return;
 
   DCHECK(animated_image_);
-  if (compositor_)
-    compositor_->RemoveAnimationObserver(this);
+  ClearCurrentCompositor();
 
   animated_image_->Stop();
   state_ = State::kStopped;
@@ -102,27 +95,21 @@ const char* AnimatedImageView::GetClassName() const {
 }
 
 void AnimatedImageView::NativeViewHierarchyChanged() {
-  // When switching a window from one display to another, the compositor
-  // associated with the widget changes.
-  AddedToWidget();
-}
-
-void AnimatedImageView::AddedToWidget() {
   ui::Compositor* compositor = GetWidget()->GetCompositor();
   DCHECK(compositor);
   if (compositor_ != compositor) {
-    if (compositor_ && compositor_->HasAnimationObserver(this))
-      compositor_->RemoveAnimationObserver(this);
-    compositor_ = compositor;
+    ClearCurrentCompositor();
+
+    // Restore the Play() state with the new compositor.
+    if (state_ == State::kPlaying)
+      SetCompositorFromWidget();
   }
 }
 
 void AnimatedImageView::RemovedFromWidget() {
   if (compositor_) {
     Stop();
-    if (compositor_->HasAnimationObserver(this))
-      compositor_->RemoveAnimationObserver(this);
-    compositor_ = nullptr;
+    ClearCurrentCompositor();
   }
 }
 
@@ -134,6 +121,22 @@ void AnimatedImageView::OnAnimationStep(base::TimeTicks timestamp) {
 void AnimatedImageView::OnCompositingShuttingDown(ui::Compositor* compositor) {
   if (compositor_ == compositor) {
     Stop();
+    ClearCurrentCompositor();
+  }
+}
+
+void AnimatedImageView::SetCompositorFromWidget() {
+  DCHECK(!compositor_);
+  auto* widget = GetWidget();
+  DCHECK(widget);
+  compositor_ = widget->GetCompositor();
+  DCHECK(!compositor_->HasAnimationObserver(this));
+  compositor_->AddAnimationObserver(this);
+}
+
+void AnimatedImageView::ClearCurrentCompositor() {
+  if (compositor_) {
+    DCHECK(compositor_->HasAnimationObserver(this));
     compositor_->RemoveAnimationObserver(this);
     compositor_ = nullptr;
   }

ui/views/controls/animated_image_view.h

@@ -48,7 +48,8 @@ class VIEWS_EXPORT AnimatedImageView : public ImageViewBase,
   void SetAnimatedImage(
       std::unique_ptr<gfx::SkiaVectorAnimation> animated_image);
 
-  // Plays the animation in loop.
+  // Plays the animation in loop and must only be called when this view has
+  // access to a widget.
   void Play();
 
   // Stops any animation and resets it to the start frame.
@@ -61,13 +62,15 @@ class VIEWS_EXPORT AnimatedImageView : public ImageViewBase,
   void OnPaint(gfx::Canvas* canvas) override;
   const char* GetClassName() const override;
   void NativeViewHierarchyChanged() override;
-  void AddedToWidget() override;
   void RemovedFromWidget() override;
 
   // Overridden from ui::CompositorAnimationObserver:
   void OnAnimationStep(base::TimeTicks timestamp) override;
   void OnCompositingShuttingDown(ui::Compositor* compositor) override;
 
+  void SetCompositorFromWidget();
+  void ClearCurrentCompositor();
+
   // Overridden from ImageViewBase:
   gfx::Size GetImageSize() const override;