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

base/memory/discardable_memory_manager.cc

Index: base/memory/discardable_memory_manager.cc
diff --git a/base/memory/discardable_memory_manager.cc b/base/memory/discardable_memory_manager.cc
index 3647b7b2f91a682d2805c2752a981ad771f99e40..d976da203c4a88494dfffa6e73dd167bee6c2c11 100644
--- a/base/memory/discardable_memory_manager.cc
+++ b/base/memory/discardable_memory_manager.cc
@@ -18,11 +18,14 @@
 DiscardableMemoryManager::DiscardableMemoryManager(
     size_t memory_limit,
     size_t soft_memory_limit,
+    size_t bytes_to_keep_under_moderate_pressure,
     TimeDelta hard_memory_limit_expiration_time)
     : allocations_(AllocationMap::NO_AUTO_EVICT),
       bytes_allocated_(0u),
       memory_limit_(memory_limit),
       soft_memory_limit_(soft_memory_limit),
+      bytes_to_keep_under_moderate_pressure_(
+          bytes_to_keep_under_moderate_pressure),
       hard_memory_limit_expiration_time_(hard_memory_limit_expiration_time) {
   BytesAllocatedChanged(bytes_allocated_);
 }
@@ -32,6 +35,20 @@
   DCHECK_EQ(0u, bytes_allocated_);
 }
 
+void DiscardableMemoryManager::RegisterMemoryPressureListener() {
+  AutoLock lock(lock_);
+  DCHECK(base::MessageLoop::current());
+  DCHECK(!memory_pressure_listener_);
+  memory_pressure_listener_.reset(new MemoryPressureListener(base::Bind(
+      &DiscardableMemoryManager::OnMemoryPressure, Unretained(this))));
+}
+
+void DiscardableMemoryManager::UnregisterMemoryPressureListener() {
+  AutoLock lock(lock_);
+  DCHECK(memory_pressure_listener_);
+  memory_pressure_listener_.reset();
+}
+
 void DiscardableMemoryManager::SetMemoryLimit(size_t bytes) {
   AutoLock lock(lock_);
   memory_limit_ = bytes;
@@ -42,6 +59,12 @@
 void DiscardableMemoryManager::SetSoftMemoryLimit(size_t bytes) {
   AutoLock lock(lock_);
   soft_memory_limit_ = bytes;
+}
+
+void DiscardableMemoryManager::SetBytesToKeepUnderModeratePressure(
+    size_t bytes) {
+  AutoLock lock(lock_);
+  bytes_to_keep_under_moderate_pressure_ = bytes;
 }
 
 void DiscardableMemoryManager::SetHardMemoryLimitExpirationTime(
@@ -54,14 +77,13 @@
   return PurgeIfNotUsedSinceHardLimitCutoffUntilWithinSoftMemoryLimit();
 }
 
-void DiscardableMemoryManager::ReduceMemoryUsageUntilWithinLimit(size_t bytes) {
-  AutoLock lock(lock_);
-  PurgeIfNotUsedSinceTimestampUntilUsageIsWithinLimitWithLockAcquired(Now(),
-                                                                      bytes);
-}
-
 void DiscardableMemoryManager::Register(Allocation* allocation, size_t bytes) {
   AutoLock lock(lock_);
+  // A registered memory listener is currently required. This DCHECK can be
+  // moved or removed if we decide that it's useful to relax this condition.
+  // TODO(reveman): Enable this DCHECK when skia and blink are able to
+  // register memory pressure listeners. crbug.com/333907
+  // DCHECK(memory_pressure_listener_);
   DCHECK(allocations_.Peek(allocation) == allocations_.end());
   allocations_.Put(allocation, AllocationInfo(bytes));
 }
@@ -160,6 +182,28 @@
   return bytes_allocated_;
 }
 
+void DiscardableMemoryManager::OnMemoryPressure(
+    MemoryPressureListener::MemoryPressureLevel pressure_level) {
+  switch (pressure_level) {
+    case MemoryPressureListener::MEMORY_PRESSURE_MODERATE:
+      PurgeUntilWithinBytesToKeepUnderModeratePressure();
+      return;
+    case MemoryPressureListener::MEMORY_PRESSURE_CRITICAL:
+      PurgeAll();
+      return;
+  }
+
+  NOTREACHED();
+}
+
+void
+DiscardableMemoryManager::PurgeUntilWithinBytesToKeepUnderModeratePressure() {
+  AutoLock lock(lock_);
+
+  PurgeIfNotUsedSinceTimestampUntilUsageIsWithinLimitWithLockAcquired(
+      Now(), bytes_to_keep_under_moderate_pressure_);
+}
+
 bool DiscardableMemoryManager::
     PurgeIfNotUsedSinceHardLimitCutoffUntilWithinSoftMemoryLimit() {
   AutoLock lock(lock_);