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..528695c04af764c014da18c6f90997af66c89ec4 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 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 +99,23 @@ class GPU_EXPORT CommandBufferHelper {
   //   the value of the token to wait for.
   void WaitForToken(int32 token);
 
+  // Returns true if the serial has passed.
+  //
+  // NOTE: This will detect wrapped serials by checking if the most significant
+  // bit of serial to check is 1 but the last read is 0, i.e. the uint32
+  // wrapped.
+  //
+  // Parameters:
+  //   the value of the serial to check whether it has passed
+  bool HasSerialPassed(uint32 serial) const {
+    uint32 last_serial = last_serial_read();
+    if (serial <= last_serial)
+      return true;
+    if (serial & 0x80000000 && !(last_serial & 0x80000000))
+      return true; // we wrapped
+    return false;
+  }
+
   // 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);
@@ -244,6 +270,11 @@ class GPU_EXPORT CommandBufferHelper {
   bool AllocateRingBuffer();
   void FreeResources();
 
+  // Get the serial number last read by the command buffer.
+  uint32 last_serial_read() const {
+    return command_buffer_->GetLastState().serial;
+  }
+
   CommandBuffer* command_buffer_;
   int32 ring_buffer_id_;
   int32 ring_buffer_size_;