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 1026 matching lines @@
         validators_.texture_internal_format_storage.AddValue(GL_RGBA16F_EXT);
         validators_.texture_internal_format_storage.AddValue(GL_RGB16F_EXT);
         validators_.texture_internal_format_storage.AddValue(GL_ALPHA16F_EXT);
         validators_.texture_internal_format_storage.AddValue(
             GL_LUMINANCE16F_EXT);
         validators_.texture_internal_format_storage.AddValue(
             GL_LUMINANCE_ALPHA16F_EXT);
     }
   }
 
+  bool have_es3_occlusion_query =
+      gl_version_info_->IsAtLeastGLES(3, 0);

[yunchao, 2016/07/12 09:32:15]

We can use the code below: 
occlusion_query_in_core_feature = IsES3Capable();

Then use occlusion_query_in_core_feature, instead of have_es3_occlusion_query to
cover both gles and OGL and other variants. 

   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");
 
-  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");
+    if (context_type_ == CONTEXT_TYPE_OPENGLES2) {
+      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;
   }
 
   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