Revert of 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 5b74705234ff6c4a2243156faa5a8fc880bede87..d16ed3e8480f933725c7f9a25444ff72c2320512 100644
--- a/base/memory/discardable_memory.h
+++ b/base/memory/discardable_memory.h
@@ -64,6 +64,14 @@
  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);