Experimental 'purging and suspending' backgrounded tabs behind the flag

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index c81e108be2fee15ac2e233e91f3a4035618ed098..de436d4698e0ca27fa3d1028a29a2dc6ce9ddcd7 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -811,6 +811,9 @@ void RenderThreadImpl::Init(
 
   service_registry()->ConnectToRemoteService(
       mojo::GetProxy(&storage_partition_service_));
+
+  is_backgrounded_ = false;
+  is_cache_purged_ = false;
 }
 
 RenderThreadImpl::~RenderThreadImpl() {
@@ -1679,10 +1682,24 @@ bool RenderThreadImpl::OnControlMessageReceived(const IPC::Message& msg) {
 void RenderThreadImpl::OnProcessBackgrounded(bool backgrounded) {
   ChildThreadImpl::OnProcessBackgrounded(backgrounded);
 
-  if (backgrounded)
+  is_backgrounded_ = backgrounded;
+  if (backgrounded) {
     renderer_scheduler_->OnRendererBackgrounded();
-  else
+  } else {
     renderer_scheduler_->OnRendererForegrounded();
+    is_cache_purged_ = false;
+  }
+}
+
+void RenderThreadImpl::OnProcessPurgeAndSuspend() {
+  ChildThreadImpl::OnProcessPurgeAndSuspend();
+  if (!is_backgrounded_)
+    return;
+  if (is_cache_purged_)
+    return;
+  // TODO(hajimehoshi): Implement purging e.g. cache (crbug/607077)
+  is_cache_purged_ = true;
+  renderer_scheduler_->SuspendRendererWhenBackgrounded();

[dcheng, 2016/05/11 17:42:22]

Sorry, to clarify my earlier comment: it seems like in task_manager.cc, we'll
never send this IPC if the renderer is still foreground. So why do we need to
call this? If we get the purge and suspend IPC message, won't the renderer
already have been backgrounded by the ChildProcessMsg_SetProcessBackgrounded
message?

[hajimehoshi, 2016/05/12 05:20:14]

I understood that checking |is_backgrounded| is not needed here, but assuming
the renderer is backgrounded, SuspendRendererWhenBackgrounded is still needed to
stop the timer queue in the renderer to prevent the return of purged cache
memory.

I was not sure if a tab becomes foregrounded again (e.g. when another tab
sharing the renderer is activated) before the purging IPC arrives to the
renderer, but this never happens, right?

[hajimehoshi, 2016/05/12 08:33:18]

OK, renamed SuspendRendererWhenBackgrounded to SuspendRenderer to clarify the
purpose. also removed |is_backgrounded_|.

 }
 
 void RenderThreadImpl::OnCreateNewFrame(FrameMsg_NewFrame_Params params) {