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

gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
index d602360c369fbf5981ce8050b6f0eeb0b74b56a8..92f2b1c62ae9ba0157c4f109717087cadad91e60 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc
@@ -2734,7 +2734,8 @@ error::Error GLES2DecoderPassthroughImpl::DoMapBufferRange(
     GLbitfield access,
     void* ptr,
     int32_t data_shm_id,
-    uint32_t data_shm_offset) {
+    uint32_t data_shm_offset,
+    uint32_t* result) {
   FlushErrors();
 
   GLbitfield filtered_access = access;
@@ -2759,6 +2760,7 @@ error::Error GLES2DecoderPassthroughImpl::DoMapBufferRange(
   void* mapped_ptr = glMapBufferRange(target, offset, size, filtered_access);
   if (FlushErrors() || mapped_ptr == nullptr) {
     // Had an error while mapping, don't copy any data
+    *result = 0;
     return error::kNoError;
   }
 
@@ -2783,6 +2785,7 @@ error::Error GLES2DecoderPassthroughImpl::DoMapBufferRange(
   resources_->mapped_buffer_map.insert(
       std::make_pair(client_buffer, mapped_buffer_info));
 
+  *result = 1;
   return error::kNoError;
 }