(Reland) Discard compositor frames from unloaded web content

cc/trees/layer_tree_host_unittest.cc

Index: cc/trees/layer_tree_host_unittest.cc
diff --git a/cc/trees/layer_tree_host_unittest.cc b/cc/trees/layer_tree_host_unittest.cc
index eaf3c4756f5047cc5fe584dd6eeeec0577950b9c..1f2059cb0c3ea1c3c1bd7d9bf17b64d037a71a42 100644
--- a/cc/trees/layer_tree_host_unittest.cc
+++ b/cc/trees/layer_tree_host_unittest.cc
@@ -7010,5 +7010,32 @@ class LayerTreeHostTestSubmitFrameResources : public LayerTreeHostTest {
 
 SINGLE_AND_MULTI_THREAD_TEST_F(LayerTreeHostTestSubmitFrameResources);
 
+// Ensure that content_source_id is propagated to the frame's metadata.
+class LayerTreeHostTestContentSourceId : public LayerTreeHostTest {
+ protected:
+  void BeginTest() override {
+    layer_tree_host()->SetContentSourceId(5);
+    PostSetNeedsCommitToMainThread();
+  }
+
+  DrawResult PrepareToDrawOnThread(LayerTreeHostImpl* host_impl,
+                                   LayerTreeHostImpl::FrameData* frame_data,
+                                   DrawResult draw_result) override {
+    EXPECT_EQ(DRAW_SUCCESS, draw_result);
+    EXPECT_EQ(5U, host_impl->active_tree()->content_source_id());
+    return draw_result;
+  }
+
+  void DisplayReceivedCompositorFrameOnThread(
+      const CompositorFrame& frame) override {
+    EXPECT_EQ(5U, frame.metadata.content_source_id);
+    EndTest();
+  }
+
+  void AfterTest() override {}
+};
+
+SINGLE_AND_MULTI_THREAD_TEST_F(LayerTreeHostTestContentSourceId);
+
 }  // namespace
 }  // namespace cc