Revert of base: Introduce an explicit call for reducing emulated discardable memory usage.

base/memory/discardable_memory_emulated.h

Index: base/memory/discardable_memory_emulated.h
diff --git a/base/memory/discardable_memory_emulated.h b/base/memory/discardable_memory_emulated.h
index d928513527ea895f1e44ebd3a0415bfe446e3319..64e99511b7caad0ec835ec9cd245f262bf100b74 100644
--- a/base/memory/discardable_memory_emulated.h
+++ b/base/memory/discardable_memory_emulated.h
@@ -19,12 +19,9 @@
   explicit DiscardableMemoryEmulated(size_t bytes);
   virtual ~DiscardableMemoryEmulated();
 
+  static void RegisterMemoryPressureListeners();
+  static void UnregisterMemoryPressureListeners();
   static bool ReduceMemoryUsage();
-
-  // TODO(reveman): Remove this as it is breaking the discardable memory design
-  // principle that implementations should not rely on information this is
-  // unavailable in kernel space. crbug.com/400423
-  BASE_EXPORT static void ReduceMemoryUsageUntilWithinLimit(size_t bytes);
 
   static void PurgeForTesting();