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

base/memory/discardable_memory_manager.h

Index: base/memory/discardable_memory_manager.h
diff --git a/base/memory/discardable_memory_manager.h b/base/memory/discardable_memory_manager.h
index a61f141c43034ecb5f1cfcec5033b8d431d884d8..94b3c55108f22715b0afcbfca019ffe92b357e9f 100644
--- a/base/memory/discardable_memory_manager.h
+++ b/base/memory/discardable_memory_manager.h
@@ -8,7 +8,6 @@
 #include "base/base_export.h"
 #include "base/containers/hash_tables.h"
 #include "base/containers/mru_cache.h"
-#include "base/memory/memory_pressure_listener.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 
@@ -60,27 +59,15 @@ namespace internal {
 // of all allocation instances (in case they need to be purged), and the total
 // amount of allocated memory (in case this forces a purge). When memory usage
 // reaches the limit, the manager purges the LRU memory.
-//
-// When notified of memory pressure, the manager either purges the LRU memory --
-// if the pressure is moderate -- or all discardable memory if the pressure is
-// critical.
 class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
  public:
   typedef DiscardableMemoryManagerAllocation Allocation;
 
   DiscardableMemoryManager(size_t memory_limit,
                            size_t soft_memory_limit,
-                           size_t bytes_to_keep_under_moderate_pressure,
                            TimeDelta hard_memory_limit_expiration_time);
   virtual ~DiscardableMemoryManager();
 
-  // Call this to register memory pressure listener. Must be called on a thread
-  // with a MessageLoop current.
-  void RegisterMemoryPressureListener();
-
-  // Call this to unregister memory pressure listener.
-  void UnregisterMemoryPressureListener();
-
   // The maximum number of bytes of memory that may be allocated before we force
   // a purge.
   void SetMemoryLimit(size_t bytes);
@@ -89,9 +76,6 @@ class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
   // limit expiration time without getting purged.
   void SetSoftMemoryLimit(size_t bytes);
 
-  // Sets the amount of memory to keep when we're under moderate pressure.
-  void SetBytesToKeepUnderModeratePressure(size_t bytes);
-
   // Sets the memory usage cutoff time for hard memory limit.
   void SetHardMemoryLimitExpirationTime(
       TimeDelta hard_memory_limit_expiration_time);
@@ -101,6 +85,10 @@ class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
   // have been used.
   bool ReduceMemoryUsage();
 
+  // This can be called to attempt to reduce memory footprint until within
+  // limit for bytes to keep under moderate pressure.
+  void ReduceMemoryUsageUntilWithinLimit(size_t bytes);
+
   // Adds the given allocation to the manager's collection.
   void Register(Allocation* allocation, size_t bytes);
 
@@ -141,14 +129,6 @@ class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
   };
   typedef HashingMRUCache<Allocation*, AllocationInfo> AllocationMap;
 
-  // This can be called as a hint that the system is under memory pressure.
-  void OnMemoryPressure(
-      MemoryPressureListener::MemoryPressureLevel pressure_level);
-
-  // Purges memory until usage is less or equal to
-  // |bytes_to_keep_under_moderate_pressure_|.
-  void PurgeUntilWithinBytesToKeepUnderModeratePressure();
-
   // Purges memory not used since |hard_memory_limit_expiration_time_| before
   // "right now" until usage is less or equal to |soft_memory_limit_|.
   // Returns true if total amount of memory is less or equal to soft memory
@@ -185,14 +165,6 @@ class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
   // notification.
   size_t soft_memory_limit_;
 
-  // Under moderate memory pressure, we will purge memory until usage is within
-  // this limit.
-  size_t bytes_to_keep_under_moderate_pressure_;
-
-  // Allows us to be respond when the system reports that it is under memory
-  // pressure.
-  scoped_ptr<MemoryPressureListener> memory_pressure_listener_;
-
   // Amount of time it takes for an allocation to become affected by
   // |soft_memory_limit_|.
   TimeDelta hard_memory_limit_expiration_time_;