gpu: Reuse transfer buffers more aggresively

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 a50dc7bfe4e4e73e4bc4ce392bc1cb85e32182be..0100c6ce3b5d6f0b9d0bdaaa260f9d377e8c3f4b 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.h
+++ b/gpu/command_buffer/client/cmd_buffer_helper.h
@@ -83,6 +83,15 @@ class GPU_EXPORT CommandBufferHelper {
   //   shutdown.
   int32 InsertToken();
 
+  // Returns true if the token has already passed.
+  // Parameters:
+  //   the value of the token to check whether it has passed
+  bool HasTokenPassed(int32 token) const {
+    if (token > token_)
+      return true;  // we wrapped
+    return last_token_read() >= token;
+  }
+
   // Waits until the token of a particular value has passed through the command
   // stream (i.e. commands inserted before that token have been executed).
   // NOTE: This will call Flush if it needs to block.
@@ -90,6 +99,11 @@ class GPU_EXPORT CommandBufferHelper {
   //   the value of the token to wait for.
   void WaitForToken(int32 token);
 
+  // Get the serial number last read by the command buffer.
+  uint32 last_serial_read() const {
+    return command_buffer_->GetLastState().serial;
+  }
+
   // Called prior to each command being issued. Waits for a certain amount of
   // space to be available. Returns address of space.
   CommandBufferEntry* GetSpace(uint32 entries);