[Blimp Engine] Adds a WindowTreeClient so that popup will have non-null paren…

blimp/engine/session/blimp_engine_session.h

Index: blimp/engine/session/blimp_engine_session.h
diff --git a/blimp/engine/session/blimp_engine_session.h b/blimp/engine/session/blimp_engine_session.h
index 1b311abe8fde1e2dbb9493f2ad69eb33693b1d7e..38c740b31b970d67cf86949f5126c60accca32e3 100644
--- a/blimp/engine/session/blimp_engine_session.h
+++ b/blimp/engine/session/blimp_engine_session.h
@@ -182,6 +182,9 @@ class BlimpEngineSession
   // Used to manage input capture.
   scoped_ptr<aura::client::DefaultCaptureClient> capture_client_;
 
+  // Used to locate null-parented windows, such as a popup.

[Wez, 2016/03/29 21:20:06]

"locate" is ambiguous; I think you mean "locate in the window hierarchy"?

Suggest: "Used to attach null-parented windows (e.g. popups) to the root
window."

[haibinlu, 2016/03/29 21:57:16]

Done.

+  scoped_ptr<aura::client::WindowTreeClient> window_tree_client_;
+
   // Only one web_contents is supported for blimp 0.5
   scoped_ptr<content::WebContents> web_contents_;