memory coordinator: Add MemoryCoordinatorClient::OnPurgeMemory()

cc/tiles/gpu_image_decode_cache.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/tiles/gpu_image_decode_cache.h"
 
 #include <inttypes.h>
 
 #include "base/debug/alias.h"
 #include "base/memory/discardable_memory_allocator.h"
@@ skipping 1243 matching lines @@
 bool GpuImageDecodeCache::DiscardableIsLockedForTesting(
     const DrawImage& image) {
   base::AutoLock lock(lock_);
   auto found = persistent_cache_.Peek(image.image()->uniqueID());
   DCHECK(found != persistent_cache_.end());
   ImageData* image_data = found->second.get();
   return image_data->decode.is_locked();
 }
 
 void GpuImageDecodeCache::OnMemoryStateChange(base::MemoryState state) {
-  switch (state) {
-    case base::MemoryState::NORMAL:
-      memory_state_ = state;
-      break;
-    case base::MemoryState::THROTTLED:
-    case base::MemoryState::SUSPENDED: {
-      memory_state_ = state;
+  memory_state_ = state;
+}
 
-      // We've just changed our memory state to a (potentially) more
-      // restrictive one. Re-enforce cache limits.
-      base::AutoLock lock(lock_);
-      EnsureCapacity(0);
-      break;
-    }
-    case base::MemoryState::UNKNOWN:
-      // NOT_REACHED.
-      break;
-  }
+void GpuImageDecodeCache::OnPurgeMemory() {
+  // We've just changed our memory state to a (potentially) more
+  // restrictive one. Re-enforce cache limits.
+  base::AutoLock lock(lock_);
+  EnsureCapacity(0);
 }
 
 }  // namespace cc