gpu: Reuse transfer buffers more aggresively

gpu/command_buffer/common/command_buffer.h

Index: gpu/command_buffer/common/command_buffer.h
diff --git a/gpu/command_buffer/common/command_buffer.h b/gpu/command_buffer/common/command_buffer.h
index 394ccf3c4f7475703e6c9bb1486f308f0b06f45a..373d33a12769b63e577b3371fd359a66f93dfc3c 100644
--- a/gpu/command_buffer/common/command_buffer.h
+++ b/gpu/command_buffer/common/command_buffer.h
@@ -24,6 +24,7 @@ class GPU_EXPORT CommandBuffer {
           get_offset(0),
           put_offset(0),
           token(-1),
+          serial(0),
           error(error::kNoError),
           context_lost_reason(error::kUnknown),
           generation(0) {
@@ -45,6 +46,10 @@ class GPU_EXPORT CommandBuffer {
     // embedded in the command buffer. The default token value is zero.
     int32 token;
 
+    // The current serial. This used by the reader to synchronize with the
+    // writer that the action associated with the serial has been completed.
+    uint32 serial;
+
     // Error status.
     error::Error error;
 
@@ -118,6 +123,9 @@ class GPU_EXPORT CommandBuffer {
   // Allows the reader to update the current token value.
   virtual void SetToken(int32 token) = 0;
 
+  // Allows the reader to update the current serial value.
+  virtual void SetSerial(uint32 serial) = 0;
+
   // Allows the reader to set the current parse error.
   virtual void SetParseError(error::Error) = 0;