Re-land: base: Fix registering of memory pressure listeners used when emulating discardable memory.

base/memory/discardable_memory_provider.h

Index: base/memory/discardable_memory_provider.h
diff --git a/base/memory/discardable_memory_provider.h b/base/memory/discardable_memory_provider.h
index 6c343c0d9299505b453ded54c58476c3091f08ef..8a0635326000afbe6f80f192065b5a8892d3a4fb 100644
--- a/base/memory/discardable_memory_provider.h
+++ b/base/memory/discardable_memory_provider.h
@@ -46,6 +46,13 @@ class BASE_EXPORT_PRIVATE DiscardableMemoryProvider {
   DiscardableMemoryProvider();
   ~DiscardableMemoryProvider();
 
+  // Call this to register memory pressure listener. Must be called on a
+  // thread with a MessageLoop current.
+  void RegisterMemoryPressureListener();
+
+  // Call this to unregister memory pressure listener.
+  void UnregisterMemoryPressureListener();
+
   // The maximum number of bytes of discardable memory that may be allocated
   // before we force a purge. If this amount is zero, it is interpreted as
   // having no limit at all.
@@ -99,7 +106,7 @@ class BASE_EXPORT_PRIVATE DiscardableMemoryProvider {
   typedef HashingMRUCache<const DiscardableMemory*, Allocation> AllocationMap;
 
   // This can be called as a hint that the system is under memory pressure.
-  void NotifyMemoryPressure(
+  void OnMemoryPressure(
       MemoryPressureListener::MemoryPressureLevel pressure_level);
 
   // Purges |bytes_to_reclaim_under_moderate_pressure_| bytes of
@@ -132,7 +139,7 @@ class BASE_EXPORT_PRIVATE DiscardableMemoryProvider {
 
   // Allows us to be respond when the system reports that it is under memory
   // pressure.
-  MemoryPressureListener memory_pressure_listener_;
+  scoped_ptr<MemoryPressureListener> memory_pressure_listener_;
 
   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryProvider);
 };