Clear observers before resetting Win:OSKDisplayManager::keyboard_detector_

Bug: 760012
Change-Id: I41397192fd7fc5ea585b4a4a11310fdef7b68fdc
Reviewed-on: https://chromium-review.googlesource.com/690749
Commit-Queue: Eugene Girard <girard@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505392}

content/browser/renderer_host/render_widget_host_view_aura.cc

@@ -779,8 +779,6 @@ void RenderWidgetHostViewAura::FocusedNodeTouched(
       ui::OnScreenKeyboardDisplayManager::GetInstance();
   DCHECK(osk_display_manager);
   if (editable && host_->GetView() && host_->delegate()) {
-    if (keyboard_observer_)
-      osk_display_manager->RemoveObserver(keyboard_observer_.get());
     keyboard_observer_.reset(new WinScreenKeyboardObserver(
         this, location_dips_screen, device_scale_factor_, window_));
     virtual_keyboard_requested_ =

ui/base/win/osk_display_manager.cc

@@ -117,7 +117,9 @@ class OnScreenKeyboardDetector {
 OnScreenKeyboardDetector::OnScreenKeyboardDetector()
     : keyboard_detector_factory_(this) {}
 
-OnScreenKeyboardDetector::~OnScreenKeyboardDetector() {}
+OnScreenKeyboardDetector::~OnScreenKeyboardDetector() {
+  ClearObservers();
+}
 
 void OnScreenKeyboardDetector::DetectKeyboard(HWND main_window) {
   main_window_ = main_window;