Fix hung renderer timer code in RenderWidgetHost (task spam bug)

content/browser/renderer_host/render_widget_host.cc

 // Copyright (c) 2011 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 "content/browser/renderer_host/render_widget_host.h"
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
@@ skipping 488 matching lines @@
     Send(new ViewMsg_Repaint(routing_id_, current_size_));
   }
 }
 
 void RenderWidgetHost::StartHangMonitorTimeout(TimeDelta delay) {
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDisableHangMonitor)) {
     return;
   }
 
-  // If we already have a timer that will expire at or before the given delay,
-  // then we have nothing more to do now.  If we have set our end time to null
-  // by calling StopHangMonitorTimeout, though, we will need to restart the
-  // timer.
+  // Set time_when_considered_hung_ if it's null.
+  Time requested_end_time = Time::Now() + delay;
+  if (time_when_considered_hung_.is_null())
+    time_when_considered_hung_ = requested_end_time;
+
+  // If we already have a timer with the same or shorter duration, then we can
+  // wait for it to finish.
   if (hung_renderer_timer_.IsRunning() &&
-      hung_renderer_timer_.GetCurrentDelay() <= delay &&
-      !time_when_considered_hung_.is_null()) {
+      hung_renderer_timer_.GetCurrentDelay() <= delay) {
+    // If time_when_considered_hung_ was null, this timer may fire early.
+    // CheckRendererIsUnresponsive handles that by calling
+    // StartHangMonitorTimeout with the remaining time.
+    // If time_when_considered_hung_ was non-null, it means we still haven't
+    // heard from the renderer so we leave time_when_considered_hung_ as is.
     return;
   }
 
   // Either the timer is not yet running, or we need to adjust the timer to
   // fire sooner.
-  time_when_considered_hung_ = Time::Now() + delay;
+  time_when_considered_hung_ = requested_end_time;
   hung_renderer_timer_.Stop();
   hung_renderer_timer_.Start(FROM_HERE, delay, this,
       &RenderWidgetHost::CheckRendererIsUnresponsive);
 }
 
 void RenderWidgetHost::RestartHangMonitorTimeout() {
   // Setting to null will cause StartHangMonitorTimeout to restart the timer.
   time_when_considered_hung_ = Time();
   StartHangMonitorTimeout(TimeDelta::FromMilliseconds(kHungRendererDelayMs));
 }
@@ skipping 930 matching lines @@
     pending_mouse_lock_request_ = false;
     if (!view_ || !view_->HasFocus()|| !view_->LockMouse()) {
       Send(new ViewMsg_LockMouse_ACK(routing_id_, false));
       return false;
     } else {
       Send(new ViewMsg_LockMouse_ACK(routing_id_, true));
       return true;
     }
   }
 }