Set DISCARDABLE_MEMORY_ALWAYS_SUPPORTED_NATIVELY to true on Android.

content/renderer/render_process_visibility_manager.cc

Index: content/renderer/render_process_visibility_manager.cc
diff --git a/content/renderer/render_process_visibility_manager.cc b/content/renderer/render_process_visibility_manager.cc
index 8231df4552174355793983775a2c2e2bbd025ecc..ed84bdfa49e938ced8e6ce1c28a129841d0403af 100644
--- a/content/renderer/render_process_visibility_manager.cc
+++ b/content/renderer/render_process_visibility_manager.cc
@@ -22,14 +22,14 @@ RenderProcessVisibilityManager* RenderProcessVisibilityManager::GetInstance() {
 }
 
 void RenderProcessVisibilityManager::WidgetVisibilityChanged(bool visible) {
-#if !defined(DISCARDABLE_MEMORY_ALWAYS_SUPPORTED_NATIVELY)
+#if !defined(SYSTEM_NATIVELY_SIGNALS_MEMORY_PRESSURE)
   num_visible_render_widgets_ += visible ? 1 : -1;
   DCHECK_LE(0, num_visible_render_widgets_);
   if (num_visible_render_widgets_ == 0) {
     // TODO(vollick): Remove this this heavy-handed approach once we're polling
     // the real system memory pressure.
     base::MemoryPressureListener::NotifyMemoryPressure(
-        base::MemoryPressureListener::MEMORY_PRESSURE_CRITICAL);
+        base::MemoryPressureListener::MEMORY_PRESSURE_MODERATE);

[jamesr, 2013/07/10 20:28:22]

this looks like a change in behavior. why?

[rmcilroy, 2013/07/11 08:57:27]

Yes, this is an intended behavior change.  I've looped you into the thread where
Ian and I discussed this, but the reason to change this call's argument is
because the MEMORY_PRESSURE_CRITICAL notification is very heavyweight (intended
for when Android is just about to kill Chrome due to lack of memory), so we do
things like emergency GCs in V8, which is not necessarily appropriate for
backgrounding a tab.  MEMORY_PRESSURE_MODERATE is more appropriate here since
that is the  notification we send on Android when a renderer process is
backgrounded (via a system notification).

[rmcilroy, 2013/07/11 09:07:38]

I also updated the CL's comment to include this change in behavior.

   }
 #endif
 }