Allow component IME extension use app.window and add 'ime' window type for app window

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index 0e07dbe03e94cafc518cad419a90bb223e21f37c..71d855168816d032ccca7d3223f33c056cca1beb 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -647,8 +647,7 @@ void RootWindowController::ActivateKeyboard(
     keyboard_controller->AddObserver(workspace_controller_->layout_manager());
     Shell::GetInstance()->delegate()->VirtualKeyboardActivated(true);
   }
-  aura::Window* parent = GetContainer(
-      kShellWindowId_VirtualKeyboardParentContainer);
+  aura::Window* parent = GetContainer(kShellWindowId_ImeWindowParentContainer);
   DCHECK(parent);
   aura::Window* keyboard_container =
       keyboard_controller->GetContainerWindow();
@@ -669,7 +668,7 @@ void RootWindowController::DeactivateKeyboard(
       keyboard_controller->GetContainerWindow();
   if (keyboard_container->GetRootWindow() == GetRootWindow()) {
     aura::Window* parent = GetContainer(
-        kShellWindowId_VirtualKeyboardParentContainer);
+        kShellWindowId_ImeWindowParentContainer);
     DCHECK(parent);
     parent->RemoveChild(keyboard_container);
     if (!keyboard::IsKeyboardUsabilityExperimentEnabled()) {
@@ -687,8 +686,7 @@ void RootWindowController::DeactivateKeyboard(
 }
 
 bool RootWindowController::IsVirtualKeyboardWindow(aura::Window* window) {
-  aura::Window* parent = GetContainer(
-      kShellWindowId_VirtualKeyboardParentContainer);
+  aura::Window* parent = GetContainer(kShellWindowId_ImeWindowParentContainer);
   return parent ? parent->Contains(window) : false;
 }
 
@@ -722,7 +720,7 @@ void RootWindowController::Init(RootWindowType root_window_type,
 
   if (root_window_type == VIRTUAL_KEYBOARD) {
     aura::Window* virtual_keyboard_parent_container = GetContainer(
-        kShellWindowId_VirtualKeyboardParentContainer);
+        kShellWindowId_ImeWindowParentContainer);
     virtual_keyboard_parent_container->SetBounds(root_window->bounds());
     shell->InitKeyboard();
     return;
@@ -1042,7 +1040,7 @@ void RootWindowController::CreateContainersInRootWindow(
   SetUsesScreenCoordinates(overlay_container);
 
   aura::Window* virtual_keyboard_parent_container = CreateContainer(
-      kShellWindowId_VirtualKeyboardParentContainer,
+      kShellWindowId_ImeWindowParentContainer,
       "VirtualKeyboardParentContainer",
       root_window);
   wm::SetSnapsChildrenToPhysicalPixelBoundary(