Use mapped memory for uploading large textures.

gpu/command_buffer/client/transfer_buffer.h

Index: gpu/command_buffer/client/transfer_buffer.h
diff --git a/gpu/command_buffer/client/transfer_buffer.h b/gpu/command_buffer/client/transfer_buffer.h
index 39e62a6c67d9431574c7ac8ce006a76785861895..e1f8e91ba43d08a046de8a4fec099f3c08f437d4 100644
--- a/gpu/command_buffer/client/transfer_buffer.h
+++ b/gpu/command_buffer/client/transfer_buffer.h
@@ -47,6 +47,8 @@ class GPU_EXPORT TransferBufferInterface {
 
   virtual RingBuffer::Offset GetOffset(void* pointer) const = 0;
 
+  virtual void DiscardBlock(void* p) = 0;
+
   virtual void FreePendingToken(void* p, unsigned int token) = 0;
 };
 
@@ -71,6 +73,7 @@ class GPU_EXPORT TransferBuffer : public TransferBufferInterface {
   void* AllocUpTo(unsigned int size, unsigned int* size_allocated) override;
   void* Alloc(unsigned int size) override;
   RingBuffer::Offset GetOffset(void* pointer) const override;
+  void DiscardBlock(void* p) override;
   void FreePendingToken(void* p, unsigned int token) override;
 
   // These are for testing.
@@ -163,6 +166,8 @@ class GPU_EXPORT ScopedTransferBufferPtr {
 
   void Release();
 
+  void Discard();
+
   void Reset(unsigned int new_size);
 
  private: