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");
+  bool have_es3_occlusion_query =
+      gl_version_info_->IsAtLeastGLES(3, 0);

[yunchao, 2016/07/04 02:22:39]

This CL is used to fix crbug 623871, I think you can add the condition
"feature_info_->IsES3Enabled()" to HandleBeginQueryEXT against the target
GL_ANY_SAMPLES_PASSED. Just like what the code do for target
GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN. 
The code revision here is not necessary. The code here introduce query as an
extension for ES2 context. but query is already a core feature in ES3, we don't
need to introduce query as en extension to ES3 context. WDYT?

[xinghua.cao, 2016/07/04 10:20:30]

Yunchao, thanks for your comment. I still think that we should export
"occlusion_query_boolean = true" when context is ES3. It can also be used when
client call GetCapabilities function. 
Ken & zhenyao, what do you think?

 
-  if (have_ext_occlusion_query_boolean ||
+  if (have_es3_occlusion_query ||
+      have_ext_occlusion_query_boolean ||
       have_arb_occlusion_query2 ||
       have_arb_occlusion_query) {
     AddExtensionString("GL_EXT_occlusion_query_boolean");

[Ken Russell (switch to Gerrit), 2016/06/29 22:29:56]

Do we want to add this extension string if we are advertising an ES 3.0 context?
I would think it should only be advetised for ES 2.0 contexts.

[xinghua.cao, 2016/07/04 10:20:30]

Done.

     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;
   }
 
   if (!workarounds_.disable_angle_instanced_arrays &&
       (extensions.Contains("GL_ANGLE_instanced_arrays") ||
@@ skipping 344 matching lines @@
   if (pos == std::string::npos) {
     extensions_ += (extensions_.empty() ? "" : " ") + str;
   }
 }
 
 FeatureInfo::~FeatureInfo() {
 }
 
 }  // namespace gles2
 }  // namespace gpu