Let DoMapBufferRange write the result integer to signal a GL error.

gpu/command_buffer/service/gles2_cmd_decoder_passthrough_handlers.cc

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/gles2_cmd_decoder_passthrough.h"
 
 namespace gpu {
 namespace gles2 {
 
 // Custom Handlers
@@ skipping 1304 matching lines @@
   if (*result != 0) {
     *result = 0;
     return error::kInvalidArguments;
   }
   uint8_t* mem =
       GetSharedMemoryAs<uint8_t*>(c.data_shm_id, c.data_shm_offset, size);
   if (!mem) {
     return error::kOutOfBounds;
   }
 
-  error::Error error = DoMapBufferRange(target, offset, size, access, mem,
-                                        c.data_shm_id, c.data_shm_offset);
+  error::Error error =
+      DoMapBufferRange(target, offset, size, access, mem, c.data_shm_id,
+                       c.data_shm_offset, result);
   if (error != error::kNoError) {
+    DCHECK(*result == 0);
     return error;
   }
 
-  *result = 1;
   return error::kNoError;
 }
 
 error::Error GLES2DecoderPassthroughImpl::HandleUnmapBuffer(
     uint32_t immediate_data_size,
     const volatile void* cmd_data) {
   const volatile gles2::cmds::UnmapBuffer& c =
       *static_cast<const volatile gles2::cmds::UnmapBuffer*>(cmd_data);
   GLenum target = static_cast<GLenum>(c.target);
   error::Error error = DoUnmapBuffer(target);
@@ skipping 1327 matching lines @@
   // TODO(geofflang): Handle PIXEL_UNPACK_BUFFER case.
   const void* data = GetSharedMemoryAs<const void*>(
       c.data_shm_id, c.data_shm_offset, image_size);
   return DoCompressedTexSubImage3D(
       target, level, xoffset, yoffset, zoffset, width, height, depth,
       format, image_size, data);
 }
 
 }  // namespace gles2
 }  // namespace gpu