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

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 62d6d5cf5b0c086775c6b408da1765e918c3eed6..20144ff25f016a50c5810892f3be265b542fc165 100644
--- a/base/memory/discardable_memory_emulated.h
+++ b/base/memory/discardable_memory_emulated.h
@@ -15,6 +15,9 @@ class DiscardableMemoryEmulated : public DiscardableMemory {
   explicit DiscardableMemoryEmulated(size_t size);
   virtual ~DiscardableMemoryEmulated();
 
+  static void RegisterMemoryPressureListeners();
+  static void UnregisterMemoryPressureListeners();
+
   static void PurgeForTesting();
 
   bool Initialize();