Add EventRewriterController as an aura::Env observer.

chrome/browser/chromeos/events/event_rewriter_controller.cc

Index: chrome/browser/chromeos/events/event_rewriter_controller.cc
diff --git a/chrome/browser/chromeos/events/event_rewriter_controller.cc b/chrome/browser/chromeos/events/event_rewriter_controller.cc
index 8b3cc5b40c8342b16b5f3756788f52cafe8c83ae..a22d8e716edfe18c845f5d7d684f28818e181721 100644
--- a/chrome/browser/chromeos/events/event_rewriter_controller.cc
+++ b/chrome/browser/chromeos/events/event_rewriter_controller.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/chromeos/events/event_rewriter_controller.h"
 
 #include "ash/shell.h"
+#include "ui/aura/env.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/events/event_source.h"
 
@@ -14,6 +15,7 @@ EventRewriterController::EventRewriterController() : initialized_(false) {
 }
 
 EventRewriterController::~EventRewriterController() {
+  aura::Env::GetInstance()->RemoveObserver(this);
   // Remove the rewriters from every root window EventSource and destroy them.
   for (EventRewriters::iterator rewriter_iter = rewriters_.begin();
        rewriter_iter != rewriters_.end();
@@ -45,6 +47,8 @@ void EventRewriterController::Init() {
        ++it) {
     AddToEventSource((*it)->GetHost()->GetEventSource());
   }
+  // Add the controller as an observer for new root windows.
+  aura::Env::GetInstance()->AddObserver(this);

[Daniel Erat, 2014/05/13 15:27:31]

can you do this in the c'tor instead? the add/remove calls are unbalanced
otherwise (e.g. creating an EventRewriterController and then destroying it
without having called Init() will result in a remove call with no corresponding
add)

 }
 
 void EventRewriterController::OnHostInitialized(aura::WindowTreeHost* host) {