Re-land: base: Introduce an explicit call for reducing emulated discardable memory usage.

base/memory/discardable_memory.h

Index: base/memory/discardable_memory.h
diff --git a/base/memory/discardable_memory.h b/base/memory/discardable_memory.h
index d16ed3e8480f933725c7f9a25444ff72c2320512..5b74705234ff6c4a2243156faa5a8fc880bede87 100644
--- a/base/memory/discardable_memory.h
+++ b/base/memory/discardable_memory.h
@@ -64,14 +64,6 @@ class BASE_EXPORT DiscardableMemory {
  public:
   virtual ~DiscardableMemory() {}
 
-  // Call this on a thread with a MessageLoop current to allow discardable
-  // memory implementations to respond to memory pressure signals.
-  static void RegisterMemoryPressureListeners();
-
-  // Call this to prevent discardable memory implementations from responding
-  // to memory pressure signals.
-  static void UnregisterMemoryPressureListeners();
-
   // Gets the discardable memory type with a given name.
   static DiscardableMemoryType GetNamedType(const std::string& name);