Discard compositor frames from unloaded web content

content/browser/renderer_host/render_widget_host_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 #include <tuple>
 
@@ skipping 1235 matching lines @@
   EXPECT_TRUE(delegate_->unresponsive_timer_fired());
 }
 
 // Test that the rendering timeout for newly loaded content fires
 // when enough time passes without receiving a new compositor frame.
 TEST_F(RenderWidgetHostTest, NewContentRenderingTimeout) {
   host_->set_new_content_rendering_delay_for_testing(
       base::TimeDelta::FromMicroseconds(10));
 
   // Test immediate start and stop, ensuring that the timeout doesn't fire.
-  host_->StartNewContentRenderingTimeout();
+  host_->StartNewContentRenderingTimeout(0);
   host_->OnFirstPaintAfterLoad();
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
       FROM_HERE, base::MessageLoop::QuitWhenIdleClosure(),
       TimeDelta::FromMicroseconds(20));
   base::RunLoop().Run();
 
   EXPECT_FALSE(host_->new_content_rendering_timeout_fired());
 
   // Test that the timer doesn't fire if it receives a stop before
   // a start.
   host_->OnFirstPaintAfterLoad();
-  host_->StartNewContentRenderingTimeout();
+  host_->StartNewContentRenderingTimeout(0);
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
       FROM_HERE, base::MessageLoop::QuitWhenIdleClosure(),
       TimeDelta::FromMicroseconds(20));
   base::RunLoop().Run();
 
   EXPECT_FALSE(host_->new_content_rendering_timeout_fired());
 
   // Test with a long delay to ensure that it does fire this time.
-  host_->StartNewContentRenderingTimeout();
+  host_->StartNewContentRenderingTimeout(0);
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
       FROM_HERE, base::MessageLoop::QuitWhenIdleClosure(),
       TimeDelta::FromMicroseconds(20));
   base::RunLoop().Run();
   EXPECT_TRUE(host_->new_content_rendering_timeout_fired());
 }
 
+// This tests that a compositor frame received with a stale content source ID
+// in its metadata is properly discarded.
+TEST_F(RenderWidgetHostTest, SwapCompositorFrameWithBadSourceId) {
+  host_->StartNewContentRenderingTimeout(100);
+  host_->OnFirstPaintAfterLoad();
+
+  // First swap a frame with an invalid ID.
+  cc::CompositorFrame frame;
+  frame.metadata.content_source_id = 99;
+  host_->OnMessageReceived(ViewHostMsg_SwapCompositorFrame(
+      0, 0, frame, std::vector<IPC::Message>()));
+  EXPECT_FALSE(
+      static_cast<TestView*>(host_->GetView())->did_swap_compositor_frame());
+
+  // Test with a valid content ID as a control.
+  frame.metadata.content_source_id = 100;

[danakj, 2017/03/02 18:12:50]

The code also accepts source id > 100. I've been wondering about it, and notice
that you don't test it here. Is that > actually important, if so it should be
tested. If not, maybe removed?

[kenrb, 2017/03/02 19:35:57]

That's a point, and I've added it to the test. The > is important because at
times the first compositor frame for a newly-loaded page can arrive at the
browser before the navigation commit message. It is racy because they are sent
by different threads. The comparison accounts for this case.

[danakj, 2017/03/02 19:56:34]

OK Thanks. A comment on the >= would be appreciated so this isn't lost in
codereview.

[kenrb, 2017/03/02 21:19:51]

Done.

+  host_->OnMessageReceived(ViewHostMsg_SwapCompositorFrame(
+      0, 0, frame, std::vector<IPC::Message>()));
+  EXPECT_TRUE(
+      static_cast<TestView*>(host_->GetView())->did_swap_compositor_frame());
+}
+
 TEST_F(RenderWidgetHostTest, TouchEmulator) {
   simulated_event_time_delta_seconds_ = 0.1;
   // Immediately ack all touches instead of sending them to the renderer.
   host_->OnMessageReceived(ViewHostMsg_HasTouchEventHandlers(0, false));
   host_->SetTouchEventEmulationEnabled(
       true, ui::GestureProviderConfigType::GENERIC_MOBILE);
   process_->sink().ClearMessages();
   view_->set_bounds(gfx::Rect(0, 0, 400, 200));
   view_->Show();
 
@@ skipping 448 matching lines @@
                                       ui::LatencyInfo());
 
 
   // Tests RWHI::ForwardWheelEventWithLatencyInfo().
   SimulateWheelEventWithLatencyInfo(-5, 0, 0, true, ui::LatencyInfo());
 
   ASSERT_FALSE(host_->input_router()->HasPendingEvents());
 }
 
 }  // namespace content