Support SetFocusedTextInputClient(NULL) in InputMethodTSF.

It turned out that the previous implementation of
InputMethodTSF did not support
InputMethodTSF::SetFocusedTextInputClient(NULL).
This CL fixes the issue.

BUG=246534

Review URL: https://chromiumcodereview.appspot.com/17546002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@208043 0039d316-1c4b-4281-b951-d872f2087c98

ui/base/ime/input_method_tsf.cc

@@ -89,6 +89,11 @@ void InputMethodTSF::SetFocusedTextInputClient(TextInputClient* client) {
   if (IsWindowFocused(client)) {
     ui::TSFBridge::GetInstance()->SetFocusedClient(
         GetAttachedWindowHandle(client), client);
+  } else if (!client) {
+    // SetFocusedTextInputClient(NULL) must be interpreted as
+    // "Remove the attached client".
+    ui::TSFBridge::GetInstance()->RemoveFocusedClient(
+        ui::TSFBridge::GetInstance()->GetFocusedTextInputClient());
   }
   InputMethodWin::SetFocusedTextInputClient(client);
 }