Consider IME is associated with the top level widget rather than child widget.

An important thing is that [NativeWidget A] owns Win32 input focus even
when [View X] is logically focused by FocusManager. As a result, an Win32
IME may want to interact with the native view of [NativeWidget A] rather
than that of [NativeWidget B]. This is why we need to call
GetTopLevelWidget() here.

Previous implementation treated [NativeWidget B] as associated with
the IME but it was wrong. This CL fixes the this confusion.

BUG=246534

Review URL: https://chromiumcodereview.appspot.com/17101019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@208018 0039d316-1c4b-4281-b951-d872f2087c98

ui/views/controls/textfield/native_textfield_views.cc

@@ -955,7 +955,18 @@ void NativeTextfieldViews::InsertChar(char16 ch, int flags) {
 }
 
 gfx::NativeWindow NativeTextfieldViews::GetAttachedWindow() const {
-  return GetWidget()->GetNativeWindow();
+  // Imagine the following hierarchy.
+  //   [NativeWidget A] - FocusManager
+  //     [View]
+  //     [NativeWidget B]
+  //       [View]
+  //         [View X]
+  // An important thing is that [NativeWidget A] owns Win32 input focus even
+  // when [View X] is logically focused by FocusManager. As a result, an Win32
+  // IME may want to interact with the native view of [NativeWidget A] rather
+  // than that of [NativeWidget B]. This is why we need to call
+  // GetTopLevelWidget() here.
+  return GetWidget()->GetTopLevelWidget()->GetNativeView();
 }
 
 ui::TextInputType NativeTextfieldViews::GetTextInputType() const {