Remove layer trees from pipeline when destroying Animator

shell/common/animator.cc

@@ -49,7 +49,10 @@ Animator::Animator(Delegate& delegate,
       weak_factory_(this) {
 }
 
-Animator::~Animator() = default;
+Animator::~Animator() {
+  // Remove all queued layer trees to ensure that Skia objects are unreffed.
+  layer_tree_pipeline_->Clear();
+}
 
 void Animator::Stop() {
   paused_ = true;

shell/common/pipeline.h

@@ -151,6 +151,12 @@ class Pipeline : public fml::RefCountedThreadSafe<Pipeline<R>> {
 
     {
       std::scoped_lock lock(queue_mutex_);
+
+      if (queue_.empty()) {
+        // Items were removed from queue in Clear after available_ was
+        // signalled.
+        return PipelineConsumeResult::NoneAvailable;
+      }
       std::tie(resource, trace_id) = std::move(queue_.front());
       queue_.pop_front();
       items_count = queue_.size();
@@ -171,6 +177,12 @@ class Pipeline : public fml::RefCountedThreadSafe<Pipeline<R>> {
                            : PipelineConsumeResult::Done;
   }
 
+  /// Remove all items from the queue.
+  void Clear() {
+    std::scoped_lock lock(queue_mutex_);
+    queue_.clear();
+  }
+
  private:
   const uint32_t depth_;
   fml::Semaphore empty_;

shell/common/shell_unittests.cc

@@ -701,9 +701,12 @@ TEST_F(ShellTest,
   auto end_frame_callback =
       [&](bool should_resubmit_frame,
           fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
-        ASSERT_TRUE(raster_thread_merger.get() != nullptr);
-        ASSERT_TRUE(should_resubmit_frame);
-        end_frame_called = true;
+        // The asserts below are only valid until DestroyShell is called
+        if (!end_frame_called) {
+          ASSERT_TRUE(raster_thread_merger.get() != nullptr);
+          ASSERT_TRUE(should_resubmit_frame);
+          end_frame_called = true;
+        }
         end_frame_latch.Signal();
       };
   auto external_view_embedder = std::make_shared<ShellTestExternalViewEmbedder>(