Tell observers of ArcInputMethod bounds the removal of InputMethodSurface.

We need to tell the observers of ArcInputMethod bounds when the input
method surface is being removed.
Without doing that, the observers can't know whether the input method
surface is still there or not.

      device to clamshell mode.

Bug: 1042549
Test: manual - show Chrome OS VK on an ARC++ app and flipping back the
Change-Id: Ib3e8fed3aa24a856c016ebcf7d3f6af2b2e2e1d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2043186
Commit-Queue: Yuichiro Hanada <yhanada@chromium.org>
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Auto-Submit: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739362}

ash/keyboard/arc/arc_input_method_surface_manager.cc

@@ -27,6 +27,9 @@ void ArcInputMethodSurfaceManager::RemoveSurface(
 
   if (input_method_surface_ == surface)
     input_method_surface_ = nullptr;
+
+  for (Observer& observer : observers_)
+    observer.OnArcInputMethodSurfaceBoundsChanged(gfx::Rect());
 }
 
 void ArcInputMethodSurfaceManager::OnTouchableBoundsChanged(

ash/keyboard/arc/arc_input_method_surface_manager_unittest.cc

@@ -94,6 +94,13 @@ TEST_F(ArcInputMethodSurfaceManagerTest, Observer) {
 
   EXPECT_EQ(2, observer.bounds_changed_calls_);
   EXPECT_EQ(gfx::Rect(), observer.last_bounds_);
+
+  // Drop InputMethodSurface should cause a bounds change call.
+  input_method_surface.reset();
+  EXPECT_EQ(3, observer.bounds_changed_calls_);
+  EXPECT_EQ(gfx::Rect(), observer.last_bounds_);
+
+  manager.RemoveObserver(&observer);
 }
 
 }  // namespace ash