cc: Lock access to |buffers_| in TestGpuMemoryBufferManager

cc/test/test_gpu_memory_buffer_manager.h

Index: cc/test/test_gpu_memory_buffer_manager.h
diff --git a/cc/test/test_gpu_memory_buffer_manager.h b/cc/test/test_gpu_memory_buffer_manager.h
index befa88f3a149db79849c57809101c939c085f180..0df87da60f19abf44bcf0145c845e1b90d8457b0 100644
--- a/cc/test/test_gpu_memory_buffer_manager.h
+++ b/cc/test/test_gpu_memory_buffer_manager.h
@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "base/synchronization/lock.h"
 #include "gpu/command_buffer/client/gpu_memory_buffer_manager.h"
 
 namespace cc {
@@ -35,6 +36,8 @@ class TestGpuMemoryBufferManager : public gpu::GpuMemoryBufferManager {
  private:
   // Buffers allocated by this manager.
   int last_gpu_memory_buffer_id_ = 1000;
+  // Use of |buffers_| must be protected by the lock.
+  base::Lock buffers_lock_;
   std::map<int, gfx::GpuMemoryBuffer*> buffers_;
 
   // Parent information for child managers.