Discard compositor frames from unloaded web content

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index 0f488d8d88c866c07413ade08acdc0fc1ff70551..45c15bf44d4435df01ee2b7ecc3736526097850a 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -294,6 +294,7 @@ RenderWidgetHostImpl::RenderWidgetHostImpl(RenderWidgetHostDelegate* delegate,
       last_event_type_(blink::WebInputEvent::Undefined),
       new_content_rendering_delay_(
           base::TimeDelta::FromMilliseconds(kNewContentRenderingDelayMs)),
+      current_content_source_id_(0),
       weak_factory_(this) {
   CHECK(delegate_);
   CHECK_NE(MSG_ROUTING_NONE, routing_id_);
@@ -1010,7 +1011,9 @@ void RenderWidgetHostImpl::StopHangMonitorTimeout() {
   RendererIsResponsive();
 }
 
-void RenderWidgetHostImpl::StartNewContentRenderingTimeout() {
+void RenderWidgetHostImpl::StartNewContentRenderingTimeout(
+    uint32_t next_source_id) {
+  current_content_source_id_ = next_source_id;
   // It is possible for a compositor frame to arrive before the browser is
   // notified about the page being committed, in which case no timer is
   // necessary.
@@ -1849,6 +1852,10 @@ bool RenderWidgetHostImpl::OnSwapCompositorFrame(
 
   latency_tracker_.OnSwapCompositorFrame(&frame.metadata.latency_info);
 
+  // Ignore this frame if its content has already been unloaded.

[enne (OOO), 2017/02/28 22:23:21]

I agree that maybe the mobile optimized and double tap support for page
shouldn't be updated if the frame is going to be dropped.  However, I do think
that the resources from the frame should be returned so that the renderer can
reuse them.

[kenrb, 2017/03/01 15:32:47]

Done.

+  if (frame.metadata.content_source_id < current_content_source_id_)
+    return false;
+
   bool is_mobile_optimized = IsMobileOptimizedFrame(frame.metadata);
   input_router_->NotifySiteIsMobileOptimized(is_mobile_optimized);
   if (touch_emulator_)