Redesigns the text input focus handling.

ui/base/ime/input_method_base.cc

Index: ui/base/ime/input_method_base.cc
diff --git a/ui/base/ime/input_method_base.cc b/ui/base/ime/input_method_base.cc
index d3b561cf78ed80f8bc7e889030a82a73fa187b23..3b5428dd6255d7bfac95f76ab9234b8a2f5ff689 100644
--- a/ui/base/ime/input_method_base.cc
+++ b/ui/base/ime/input_method_base.cc
@@ -10,6 +10,8 @@
 #include "ui/base/ime/input_method_delegate.h"
 #include "ui/base/ime/input_method_observer.h"
 #include "ui/base/ime/text_input_client.h"
+#include "ui/base/ime/text_input_focus_manager.h"
+#include "ui/base/ui_base_switches_util.h"
 #include "ui/events/event.h"
 
 namespace ui {
@@ -56,6 +58,9 @@ void InputMethodBase::DetachTextInputClient(TextInputClient* client) {
 }
 
 TextInputClient* InputMethodBase::GetTextInputClient() const {
+  if (switches::IsNewTextInputFocusEnabled())
+    return TextInputFocusManager::GetInstance()->GetFocusedTextInputClient();
+
   return system_toplevel_window_focused_ ? text_input_client_ : NULL;
 }
 
@@ -123,6 +128,9 @@ void InputMethodBase::NotifyTextInputStateChanged(
 
 void InputMethodBase::SetFocusedTextInputClientInternal(
     TextInputClient* client) {
+  if (switches::IsNewTextInputFocusEnabled())
+    return;

[msw, 2014/03/11 00:58:50]

Will the input methods still work okay without calling
On[Will|Did]ChangeFocusedClient and NotifyTextInputStateChanged? Those seem to
cancel/confirm compositions, update other internal state, and notify input
method observers.

[Yuki, 2014/03/11 15:27:37]

It's okay.  views::FocusManager::{Focus,Blur}TextInputClient() take care of
those things.  We'll no longer need those methods.  They'll be removed in
future, and InputMethod will be simplified.

[msw, 2014/03/11 23:24:37]

Sounds good.

+
   TextInputClient* old = text_input_client_;
   if (old == client)
     return;