Use mapped memory for uploading large textures.

gpu/command_buffer/client/ring_buffer.h

Index: gpu/command_buffer/client/ring_buffer.h
diff --git a/gpu/command_buffer/client/ring_buffer.h b/gpu/command_buffer/client/ring_buffer.h
index dfe16f7326e2f762817ac90c8bfaecc385714202..00de8a59badda7e27dd62eff1fb4b55b6224d563 100644
--- a/gpu/command_buffer/client/ring_buffer.h
+++ b/gpu/command_buffer/client/ring_buffer.h
@@ -54,6 +54,12 @@ class GPU_EXPORT RingBuffer {
   //   token: the token value to wait for before re-using the memory.
   void FreePendingToken(void* pointer, unsigned int token);
 
+  // Discards a block within the ring buffer.
+  //
+  // Parameters:
+  //   pointer: the pointer to the memory block to free.
+  void DiscardBlock(void* pointer);
+
   // Gets the size of the largest free block that is available without waiting.
   unsigned int GetLargestFreeSizeNoWaiting();