Fix for crbug.com/111185.

content/browser/renderer_host/render_widget_host.cc

Index: content/browser/renderer_host/render_widget_host.cc
diff --git a/content/browser/renderer_host/render_widget_host.cc b/content/browser/renderer_host/render_widget_host.cc
index 644eca8a47e6df1c778aea1522e3db1ff391a028..495056e25dd8ff72f3b1de5b01850884376ff7b5 100644
--- a/content/browser/renderer_host/render_widget_host.cc
+++ b/content/browser/renderer_host/render_widget_host.cc
@@ -77,6 +77,7 @@ bool ShouldCoalesceMouseWheelEvents(const WebMouseWheelEvent& last_event,
 RenderWidgetHost::RenderWidgetHost(content::RenderProcessHost* process,
                                    int routing_id)
     : renderer_initialized_(false),
+      hung_renderer_delay_ms_(kHungRendererDelayMs),
       renderer_accessible_(false),
       view_(NULL),
       process_(process),
@@ -94,6 +95,7 @@ RenderWidgetHost::RenderWidgetHost(content::RenderProcessHost* process,
       touch_event_is_queued_(false),
       needs_repainting_on_restore_(false),
       is_unresponsive_(false),
+      in_flight_event_count_(0),
       in_get_backing_store_(false),
       view_being_painted_(false),
       ignore_input_events_(false),
@@ -538,13 +540,13 @@ void RenderWidgetHost::StartHangMonitorTimeout(TimeDelta delay) {
 void RenderWidgetHost::RestartHangMonitorTimeout() {
   // Setting to null will cause StartHangMonitorTimeout to restart the timer.
   time_when_considered_hung_ = Time();
-  StartHangMonitorTimeout(TimeDelta::FromMilliseconds(kHungRendererDelayMs));
+  StartHangMonitorTimeout(
+      TimeDelta::FromMilliseconds(hung_renderer_delay_ms_));
 }
 
 void RenderWidgetHost::StopHangMonitorTimeout() {
   time_when_considered_hung_ = Time();
   RendererIsResponsive();
-
   // We do not bother to stop the hung_renderer_timer_ here in case it will be
   // started again shortly, which happens to be the common use case.
 }
@@ -719,7 +721,9 @@ void RenderWidgetHost::ForwardInputEvent(const WebInputEvent& input_event,
   // after this line.
   next_mouse_move_.reset();
 
-  StartHangMonitorTimeout(TimeDelta::FromMilliseconds(kHungRendererDelayMs));
+  in_flight_event_count_++;
+  StartHangMonitorTimeout(
+      TimeDelta::FromMilliseconds(hung_renderer_delay_ms_));
 }
 
 void RenderWidgetHost::ForwardTouchEvent(
@@ -770,6 +774,9 @@ void RenderWidgetHost::RendererExited(base::TerminationStatus status,
   is_hidden_ = false;
   is_accelerated_compositing_active_ = false;
 
+  // Reset this to ensure the hung renderer mechanism is working properly.
+  in_flight_event_count_ = 0;
+
   if (view_) {
     view_->RenderViewGone(status, exit_code);
     view_ = NULL;  // The View should be deleted by RenderViewGone.
@@ -1149,7 +1156,13 @@ void RenderWidgetHost::OnMsgInputEventAck(WebInputEvent::Type event_type,
   UMA_HISTOGRAM_TIMES("MPArch.RWH_InputEventDelta", delta);
 
   // Cancel pending hung renderer checks since the renderer is responsive.
-  StopHangMonitorTimeout();
+  if (--in_flight_event_count_ == 0 ||
+      !CommandLine::ForCurrentProcess()->HasSwitch(

[darin (slow to review), 2012/01/24 20:06:56]

I still don't quite understand the need for checking this command line flag.

+            switches::kEnableThreadedCompositing)) {
+    // TODO: don't check for kEnableThreadedCompositing when
+    // the compositor thread is used by default.
+    StopHangMonitorTimeout();
+  }
 
   int type = static_cast<int>(event_type);
   if (type < WebInputEvent::Undefined) {