Occlusion query feature is already in GL ES3.0 spec, not an extension.

gpu/command_buffer/service/feature_info.cc

 // Copyright (c) 2012 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/feature_info.h"
 
 #include <stddef.h>
 
 #include <set>
 #include <vector>
@@ skipping 1035 matching lines @@
             GL_LUMINANCE_ALPHA16F_EXT);
     }
   }
 
   bool have_ext_occlusion_query_boolean =
       extensions.Contains("GL_EXT_occlusion_query_boolean");
   bool have_arb_occlusion_query2 =
       extensions.Contains("GL_ARB_occlusion_query2");
   bool have_arb_occlusion_query =
       extensions.Contains("GL_ARB_occlusion_query");
 

[xinghua.cao, 2016/06/28 10:19:15]

On mesa+i965 platform, supports OpenGL ES 3.1, it has not any extension of
GL_EXT_occlusion_query_boolean, GL_ARB_occlusion_query2, GL_ARB_occlusion_query.
So the query feature cannot work correctly in command buffer, but I think it is
standard feature for ES3.0. If driver version is above ES3.0 (or high OpenGL
version), occlusion_query_boolean should be true.

+  if (IsES3Capable()) {
+    feature_flags_.occlusion_query_boolean = true;
+  }

[Zhenyao Mo, 2016/06/28 17:59:05]

I think you need to be more careful in these settings here.

If it's ES3Capable, you should set occlusion_qerry_boolean and
use_arb_occlusion_query_for_occlusion_query_boolean to true, and
use_arb_occlusion_query2_for_occlusion_query_boolean remains false. else, then
you need to set the above three bools and do the if block below.

[Ken Russell (switch to Gerrit), 2016/06/28 23:58:59]

Not sure about that. Is Intel's driver OpenGL ES rather than OpenGL?

There should probably be a new bool "have_es3_occlusion_query" and it should be
integrated into the block below. It should be predicated not on IsES3Capable(),
but rather on something like gl_version_info().IsAtLeastGLES(3, 0).

[Zhenyao Mo, 2016/06/29 00:39:44]

My original suggestion was to always map to the ES3 semantics whenever possible.
Ken's idea should work too. Probably safer than mine.

[xinghua.cao, 2016/06/29 10:40:09]

It is Intel's driver OpenGL ES. I had changed it, please help to reivew it
again, thank you. 

   if (have_ext_occlusion_query_boolean ||
       have_arb_occlusion_query2 ||
       have_arb_occlusion_query) {
     AddExtensionString("GL_EXT_occlusion_query_boolean");
     feature_flags_.occlusion_query_boolean = true;
     feature_flags_.use_arb_occlusion_query2_for_occlusion_query_boolean =
         !have_ext_occlusion_query_boolean && have_arb_occlusion_query2;
     feature_flags_.use_arb_occlusion_query_for_occlusion_query_boolean =
         !have_ext_occlusion_query_boolean && have_arb_occlusion_query &&
         !have_arb_occlusion_query2;
@@ skipping 348 matching lines @@
   if (pos == std::string::npos) {
     extensions_ += (extensions_.empty() ? "" : " ") + str;
   }
 }
 
 FeatureInfo::~FeatureInfo() {
 }
 
 }  // namespace gles2
 }  // namespace gpu