Experimental 'purging and suspending' backgrounded tabs behind the flag

components/scheduler/renderer/renderer_scheduler_impl.cc

 // Copyright 2014 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 "components/scheduler/renderer/renderer_scheduler_impl.h"
 
 #include "base/bind.h"
 #include "base/debug/stack_trace.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 366 matching lines @@
                "RendererSchedulerImpl::OnRendererForegrounded");
   helper_.CheckOnValidThread();
   if (helper_.IsShutdown() || !MainThreadOnly().renderer_backgrounded)
     return;
 
   MainThreadOnly().renderer_backgrounded = false;
   suspend_timers_when_backgrounded_closure_.Cancel();
   ResumeTimerQueueWhenForegrounded();
 }
 
+void RendererSchedulerImpl::OnRendererPurgeAndSuspend() {
+  helper_.CheckOnValidThread();
+  if (helper_.IsShutdown() || !MainThreadOnly().renderer_backgrounded)

[Sami, 2016/04/27 15:44:43]

We should probably cancel suspend_timers_when_backgrounded_closure_ here because
this is doing essentially the same thing.

[hajimehoshi, 2016/04/28 10:26:58]

Done.

+    return;
+  // TODO(hajimehoshi): Implement purging e.g. cache (crbug/607077)

[Sami, 2016/04/27 15:44:43]

Have you thought about what kind of interfaces would you need to implement
purging? Since this is in components it might be a little awkward. (One proposal
has been to move RendererScheduler to blink/platform, but so far we haven't
investigated it too deeply.)

[hajimehoshi, 2016/04/28 10:26:58]

Right. Moved this comment to RenderThreadImpl and changed the scheduler to do
only suspending. Done.

+  SuspendTimerQueueWhenBackgrounded();

[Sami, 2016/04/27 15:44:43]

We should think about whether we need to suspend other task sources such as
network tasks and perhaps postMessages.

[hajimehoshi, 2016/04/28 10:26:58]

Good point, we might need to do what you suggest. However, we expect suspending
only the timer queue will stop not all but most of layout and JavaScript. I'll
revisit this when needed since this is just an experiment.

+}
+
 void RendererSchedulerImpl::EndIdlePeriod() {
   if (MainThreadOnly().in_idle_period_for_testing)
     return;
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"),
                "RendererSchedulerImpl::EndIdlePeriod");
   helper_.CheckOnValidThread();
   idle_helper_.EndIdlePeriod();
 }
 
 void RendererSchedulerImpl::EndIdlePeriodForTesting(
@@ skipping 848 matching lines @@
     }
     MainThreadOnly().have_reported_blocking_intervention_since_navigation =
         true;
     BroadcastConsoleWarning(
         "Deferred long-running timer task(s) to improve scrolling smoothness. "
         "See crbug.com/574343.");
   }
 }
 
 }  // namespace scheduler