[Not for review] Discardable memory emulation

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 9b7524af4a21da31d78ae81f15c2b08da7e478ed..f67efccd7051b8150ae5b802ce2d64bb051cf39e 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -118,6 +118,12 @@
 #include "third_party/webrtc/system_wrappers/interface/event_tracer.h"
 #endif
 
+#if !defined(OS_ANDROID) && !defined(OS_MACOSX)
+#include "base/memory/discardable_memory.h"
+#include "content/renderer/render_process_discardable_memory_provider.h"
+#include "content/renderer/render_process_visibility_manager.h"
+#endif
+
 using base::ThreadRestrictions;
 using WebKit::WebDocument;
 using WebKit::WebFrame;
@@ -404,6 +410,13 @@ void RenderThreadImpl::Init() {
     RegisterExtension(MemoryBenchmarkingExtension::Get());
 #endif  // USE_TCMALLOC
 
+#if !defined(OS_ANDROID) && !defined(OS_MACOSX)
+  discardable_provider_.reset(new RenderProcessDiscardableMemoryProvider);
+  RenderProcessVisibilityManager::GetInstance()->AddObserver(
+      discardable_provider_.get());

[jonathan.backer, 2013/05/29 14:02:54]

I don't see the advantage of a singleton here.  RenderProcessVisibilityManager
is only referenced from inside RenderThreadImpl. Maybe RenderThreadImpl can own
it.

Right now, there is a bit of a life-time issue with the Manager and Provider. I
think that you're leaking both (which is fine). But if Manager is no longer a
singleton, you'll want to tighten this up.

Maybe Manager owns Provider/is a Provider?

+  base::DiscardableMemory::SetProvider(discardable_provider_.get());

[jonathan.backer, 2013/05/29 14:02:54]

I suspect that you may have many RenderThreadImpls per render process (multiple
tabs per process). In which case you'll have to rework SetProvider.

+#endif
+
   if (command_line.HasSwitch(switches::kEnableSkiaBenchmarking)) {
     LOG(WARNING) << "Enabling unsafe Skia benchmarking extension.";
     RegisterExtension(SkiaBenchmarkingExtension::Get());
@@ -621,6 +634,10 @@ void RenderThreadImpl::WidgetHidden() {
   DCHECK(hidden_widget_count_ < widget_count_);
   hidden_widget_count_++;
 
+#if !defined(OS_ANDROID) && !defined(OS_MACOSX)
+  RenderProcessVisibilityManager::GetInstance()->WidgetVisibilityChanged(false);
+#endif
+
   if (!GetContentClient()->renderer()->RunIdleHandlerWhenWidgetsHidden()) {
     return;
   }
@@ -632,6 +649,11 @@ void RenderThreadImpl::WidgetHidden() {
 void RenderThreadImpl::WidgetRestored() {
   DCHECK_GT(hidden_widget_count_, 0);
   hidden_widget_count_--;
+
+#if !defined(OS_ANDROID) && !defined(OS_MACOSX)
+  RenderProcessVisibilityManager::GetInstance()->WidgetVisibilityChanged(true);
+#endif
+
   if (!GetContentClient()->renderer()->RunIdleHandlerWhenWidgetsHidden()) {
     return;
   }