memory coordinator: Add MemoryCoordinatorClient::OnPurgeMemory()

cc/raster/staging_buffer_pool.cc

Index: cc/raster/staging_buffer_pool.cc
diff --git a/cc/raster/staging_buffer_pool.cc b/cc/raster/staging_buffer_pool.cc
index ef78e4d317e60f4a8f3b3b5ca1298a05446fb60d..6fa0fe03551d7604e93fdd6a5c89a2f502704a5e 100644
--- a/cc/raster/staging_buffer_pool.cc
+++ b/cc/raster/staging_buffer_pool.cc
@@ -432,24 +432,10 @@ void StagingBufferPool::ReleaseBuffersNotUsedSince(base::TimeTicks time) {
   }
 }
 
-void StagingBufferPool::OnMemoryStateChange(base::MemoryState state) {
-  switch (state) {
-    case base::MemoryState::NORMAL:
-      // TODO(tasak): go back to normal state.
-      break;
-    case base::MemoryState::THROTTLED:
-      // TODO(tasak): make the limits of this component's caches smaller to
-      // save memory usage.
-      break;
-    case base::MemoryState::SUSPENDED: {
-      base::AutoLock lock(lock_);
-      // Release all buffers, regardless of how recently they were used.
-      ReleaseBuffersNotUsedSince(base::TimeTicks() + base::TimeDelta::Max());
-    } break;
-    case base::MemoryState::UNKNOWN:
-      // NOT_REACHED.
-      break;
-  }
+void StagingBufferPool::OnPurgeMemory() {
+  base::AutoLock lock(lock_);
+  // Release all buffers, regardless of how recently they were used.
+  ReleaseBuffersNotUsedSince(base::TimeTicks() + base::TimeDelta::Max());
 }
 
 }  // namespace cc