Increase GPU transfer buffer alignment to 16 bytes.

This might help improve the performance of copies from the buffer, particularly inside UpdateSubresource in the GPU driver.

BUG=524305

Review URL: https://codereview.chromium.org/1635183003

Cr-Commit-Position: refs/heads/master@{#372250}

gpu/command_buffer/client/gles2_implementation.h

@@ -158,7 +158,7 @@ class GLES2_IMPL_EXPORT GLES2Implementation
   static const uint32_t kResultBucketId = 1;
 
   // Alignment of allocations.
-  static const unsigned int kAlignment = 4;
+  static const unsigned int kAlignment = 16;
 
   // GL names for the buffers used to emulate client side buffers.
   static const GLuint kClientSideArrayId = 0xFEDCBA98u;