base: Refactor DiscardableMemoryProvider to build and be tested on all platforms.

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 ea887a302d64b3e99ad5ec1f9df2fc530255bc02..6c343c0d9299505b453ded54c58476c3091f08ef 100644
--- a/base/memory/discardable_memory_provider.h
+++ b/base/memory/discardable_memory_provider.h
@@ -46,14 +46,6 @@ class BASE_EXPORT_PRIVATE DiscardableMemoryProvider {
   DiscardableMemoryProvider();
   ~DiscardableMemoryProvider();
 
-  static DiscardableMemoryProvider* GetInstance();
-
-  // Sets the instance of DiscardableMemoryProvider to be returned by
-  // GetInstance. This should only be used by tests and must be called
-  // prior to GetInstance(). The ownership of the given provider is
-  // retained by the caller.
-  static void SetInstanceForTest(DiscardableMemoryProvider* provider);
-
   // 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.
@@ -107,7 +99,7 @@ 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.
-  static void NotifyMemoryPressure(
+  void NotifyMemoryPressure(
       MemoryPressureListener::MemoryPressureLevel pressure_level);
 
   // Purges |bytes_to_reclaim_under_moderate_pressure_| bytes of