winaura: Do not create WindowObservers for BrowserPlugin.

content/browser/web_contents/web_contents_view_aura.cc

Index: content/browser/web_contents/web_contents_view_aura.cc
diff --git a/content/browser/web_contents/web_contents_view_aura.cc b/content/browser/web_contents/web_contents_view_aura.cc
index 782d57e86482dd8835aafd9d8a88931b427dcc47..477bc472235de4dbcaf8d322bdf0ece152162cdd 100644
--- a/content/browser/web_contents/web_contents_view_aura.cc
+++ b/content/browser/web_contents/web_contents_view_aura.cc
@@ -1219,7 +1219,13 @@ void WebContentsViewAura::CreateView(
   window_->layer()->SetMasksToBounds(true);
   window_->SetName("WebContentsViewAura");
 
-  window_observer_.reset(new WindowObserver(this));
+  // WindowObserver is not interesting and is problematic for Browser Plugin
+  // guests.
+  // The use cases for WindowObserver do not apply to Browser Plugins:
+  // 1) guests do not support NPAPI plugins.
+  // 2) guests' window bounds are supposed to come from its embedder.
+  if (!web_contents_->GetRenderProcessHost()->IsGuest())
+    window_observer_.reset(new WindowObserver(this));
 
   // delegate_->GetDragDestDelegate() creates a new delegate on every call.
   // Hence, we save a reference to it locally. Similar model is used on other