(not for commit) Simplified multi-threaded Ganesh with lock on Flush only.

gpu/command_buffer/client/cmd_buffer_helper.h

Index: gpu/command_buffer/client/cmd_buffer_helper.h
diff --git a/gpu/command_buffer/client/cmd_buffer_helper.h b/gpu/command_buffer/client/cmd_buffer_helper.h
index 053c1c9f2a9e5e2b0cd570e5631921575546b966..5799874ee6dbf3108232b94addc10521e8af99a4 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.h
+++ b/gpu/command_buffer/client/cmd_buffer_helper.h
@@ -10,6 +10,7 @@
 #include <string.h>
 #include <time.h>
 
+#include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "gpu/command_buffer/common/cmd_buffer_common.h"
 #include "gpu/command_buffer/common/command_buffer.h"
@@ -71,6 +72,9 @@ class GPU_EXPORT CommandBufferHelper {
   // disconnected.
   bool Finish();
 
+  void SetSafeFlushPoint();
+  void SafeFlush();
+
   // Waits until a given number of available entries are available.
   // Parameters:
   //   count: number of entries needed. This value must be at most
@@ -320,8 +324,10 @@ class GPU_EXPORT CommandBufferHelper {
   int32 total_entry_count_;  // the total number of entries
   int32 immediate_entry_count_;
   int32 token_;
+  base::Lock flush_lock_;
   int32 put_;
   int32 last_put_sent_;
+  int32 safe_put_point_;
 
 #if defined(CMD_HELPER_PERIODIC_FLUSH_CHECK)
   int commands_issued_;