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

gpu/command_buffer/service/feature_info.cc

Index: gpu/command_buffer/service/feature_info.cc
diff --git a/gpu/command_buffer/service/feature_info.cc b/gpu/command_buffer/service/feature_info.cc
index dafa6caccd71a3c2772943f7ecc79212d51b26f4..413e11d39f10a84c9707f07f8cdd999aa20933dc 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -1044,6 +1044,8 @@ void FeatureInfo::InitializeFeatures() {
     }
   }
 
+  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 =
@@ -1051,10 +1053,13 @@ void FeatureInfo::InitializeFeatures() {
   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;