arc: Use exo::WMHelper to abserve window focus.

components/arc/ime/arc_ime_service.cc

Index: components/arc/ime/arc_ime_service.cc
diff --git a/components/arc/ime/arc_ime_service.cc b/components/arc/ime/arc_ime_service.cc
index dd10ba9170642799c66ce96c68f2eb632e3be281..eeeeb5eeb1024fdf520403eab548e0e10cdb3597 100644
--- a/components/arc/ime/arc_ime_service.cc
+++ b/components/arc/ime/arc_ime_service.cc
@@ -11,7 +11,6 @@
 #include "components/arc/ime/arc_ime_bridge_impl.h"
 #include "components/exo/shell_surface.h"
 #include "components/exo/surface.h"
-#include "ui/aura/client/focus_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_tree_host.h"
@@ -42,9 +41,9 @@ ArcImeService::ArcImeService(ArcBridgeService* bridge_service)
       ime_bridge_(new ArcImeBridgeImpl(this, bridge_service)),
       ime_type_(ui::TEXT_INPUT_TYPE_NONE),
       has_composition_text_(false),
-      focus_client_(nullptr),
       keyboard_controller_(nullptr),
-      test_input_method_(nullptr) {
+      test_input_method_(nullptr),
+      is_focus_observer_installed_(false) {
   aura::Env* env = aura::Env::GetInstanceDontCreate();
   if (env)
     env->AddObserver(this);
@@ -55,10 +54,8 @@ ArcImeService::~ArcImeService() {
   if (input_method)
     input_method->DetachTextInputClient(this);
 
-  for (aura::Window* window : arc_windows_.windows())
-    window->RemoveObserver(this);
-  if (focus_client_)
-    focus_client_->RemoveObserver(this);
+  if (is_focus_observer_installed_ && exo::WMHelper::GetInstance())

[Yusuke Sato, 2016/08/20 01:25:38]

Is the is_focus_observer_installed_ check really necessary? base::ObserverList
just ignores unknown pointers.

[Peng, 2016/08/20 13:09:23]

As I explained at line 94. It is difficult to remove
is_focus_observer_installed_, so checking it here shouldn't hurt anything. 

+    exo::WMHelper::GetInstance()->RemoveFocusObserver(this);
   aura::Env* env = aura::Env::GetInstanceDontCreate();
   if (env)
     env->RemoveObserver(this);
@@ -93,8 +90,10 @@ ui::InputMethod* ArcImeService::GetInputMethod() {
 
 void ArcImeService::OnWindowInitialized(aura::Window* new_window) {
   if (IsArcWindow(new_window)) {
-    arc_windows_.Add(new_window);
-    new_window->AddObserver(this);
+    if (!is_focus_observer_installed_) {
+      exo::WMHelper::GetInstance()->AddFocusObserver(this);

[Yusuke Sato, 2016/08/20 01:25:38]

Can't we move this to somewhere else (e.g. the constructor) which is executed
only once so we can remove is_focus_observer_installed_ member variable?

[Peng, 2016/08/20 13:09:23]

The constructor doesn't work, because this class is created before exo
initialization. That why we have to delay the observer installation to here.

+      is_focus_observer_installed_ = true;
+    }
   }
   keyboard::KeyboardController* keyboard_controller =
       keyboard::KeyboardController::GetInstance();
@@ -105,23 +104,8 @@ void ArcImeService::OnWindowInitialized(aura::Window* new_window) {
   }
 }
 
-void ArcImeService::OnWindowAddedToRootWindow(aura::Window* window) {
-  aura::Window* root = window->GetRootWindow();
-  aura::client::FocusClient* focus_client = aura::client::GetFocusClient(root);
-  if (!focus_client)
-    return;
-
-  if (focus_client_) {
-    // Root windows share the same FocusClient in Ash.
-    DCHECK_EQ(focus_client_, focus_client);
-  } else {
-    focus_client_ = focus_client;
-    focus_client_->AddObserver(this);
-  }
-}
-
 ////////////////////////////////////////////////////////////////////////////////
-// Overridden from aura::client::FocusChangeObserver:
+// Overridden from exo::WMHelper::FocusChangeObserver:
 
 void ArcImeService::OnWindowFocused(aura::Window* gained_focus,
                                    aura::Window* lost_focus) {