Make ShareGroup thread safe

gpu/command_buffer/client/atomicops.h

Index: gpu/command_buffer/client/atomicops.h
diff --git a/gpu/command_buffer/client/atomicops.h b/gpu/command_buffer/client/atomicops.h
index ffd274cf2a52ebbe4ac11de89c661d3c91d926c1..7fa68bdb9d8f3993827cc42cfe0aa1ffbb807b7b 100644
--- a/gpu/command_buffer/client/atomicops.h
+++ b/gpu/command_buffer/client/atomicops.h
@@ -5,10 +5,47 @@
 #ifndef GPU_COMMAND_BUFFER_CLIENT_ATOMICOPS_H_
 #define GPU_COMMAND_BUFFER_CLIENT_ATOMICOPS_H_
 
+#include "../../gpu_export.h"
+#include "../common/scoped_ptr.h"
+#include "../common/types.h"
+
 namespace gpu {
 
 void MemoryBarrier();
 
+class LockImpl;
+class GPU_EXPORT Lock {
+ public:
+  Lock();
+  ~Lock();
+  void Acquire();
+  void Release();
+  bool Try();
+  void AssertAcquired() const;
+
+ private:
+  scoped_ptr<LockImpl> lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(Lock);
+};
+
+// A helper class that acquires the given Lock while the AutoLock is in scope.
+class GPU_EXPORT AutoLock {
+ public:
+  explicit AutoLock(Lock& lock) : lock_(lock) {
+    lock_.Acquire();
+  }
+
+  ~AutoLock() {
+    lock_.AssertAcquired();
+    lock_.Release();
+  }
+
+ private:
+  Lock& lock_;
+  DISALLOW_COPY_AND_ASSIGN(AutoLock);
+};
+
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_ATOMICOPS_H_