Add support for GL_CHROMIUM_pixel_transfer_buffer_object.

gpu/command_buffer/build_gles2_cmd_buffer.py

Index: gpu/command_buffer/build_gles2_cmd_buffer.py
diff --git a/gpu/command_buffer/build_gles2_cmd_buffer.py b/gpu/command_buffer/build_gles2_cmd_buffer.py
index ccdbc4eb53f9a3bc8309da9bfe9f299323fa8709..77ab9cbdd48a12b8f0cbefcbbf9fb0af14f4665d 100755
--- a/gpu/command_buffer/build_gles2_cmd_buffer.py
+++ b/gpu/command_buffer/build_gles2_cmd_buffer.py
@@ -93,6 +93,8 @@ _ENUM_LISTS = {
     'valid': [
       'GL_ARRAY_BUFFER',
       'GL_ELEMENT_ARRAY_BUFFER',
+      'GL_PIXEL_PACK_TRANSFER_BUFFER_CHROMIUM',
+      'GL_PIXEL_UNPACK_TRANSFER_BUFFER_CHROMIUM',
     ],
     'invalid': [
       'GL_RENDERBUFFER',
@@ -166,6 +168,8 @@ _ENUM_LISTS = {
       'GL_NUM_COMPRESSED_TEXTURE_FORMATS',
       'GL_NUM_SHADER_BINARY_FORMATS',
       'GL_PACK_ALIGNMENT',
+      'GL_PIXEL_PACK_TRANSFER_BUFFER_BINDING_CHROMIUM',
+      'GL_PIXEL_UNPACK_TRANSFER_BUFFER_BINDING_CHROMIUM',
       'GL_POLYGON_OFFSET_FACTOR',
       'GL_POLYGON_OFFSET_FILL',
       'GL_POLYGON_OFFSET_UNITS',