Use the extensions generated by FeatureInfo in the passthrough cmd decoder.

gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.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"
 
 #include "base/strings/string_number_conversions.h"
 
 namespace gpu {
 namespace gles2 {
@@ skipping 1128 matching lines @@
     case GL_SHADING_LANGUAGE_VERSION:
       *result = GetServiceShadingLanguageVersionString(feature_info_.get());
       break;
     case GL_RENDERER:
       *result = GetServiceRendererString(feature_info_.get());
       break;
     case GL_VENDOR:
       *result = GetServiceVendorString(feature_info_.get());
       break;
     case GL_EXTENSIONS:
-      *result = extension_string_.c_str();
+      *result = feature_info_->extensions().c_str();
       break;
     default:
       *result = reinterpret_cast<const char*>(glGetString(name));
       break;
   }
 
   return error::kNoError;
 }
 
 error::Error GLES2DecoderPassthroughImpl::DoGetSynciv(GLuint sync,
@@ skipping 2075 matching lines @@
 GLES2DecoderPassthroughImpl::DoUniformMatrix4fvStreamTextureMatrixCHROMIUM(
     GLint location,
     GLboolean transpose,
     const volatile GLfloat* defaultValue) {
   NOTIMPLEMENTED();
   return error::kNoError;
 }
 
 }  // namespace gles2
 }  // namespace gpu