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 0371fb15e5dd1d87ba7526d07c868ff6b0e16fb9..8fc1318c7bb88bedd7d6cba1824e870074e74d2f 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -1053,8 +1053,11 @@ void FeatureInfo::InitializeFeatures() {
       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.