Use guest's existing GestureRecognizer instead of global one.

This makes touch events work in <webview>.
Otherwise GestureRecognizer starts sending event to bogus Window*, which
crashes the browser.

BUG=413017
Test=
In a touch enabled device, open a chrome app that has a <webview>.
e.g. https://chrome.google.com/webstore/detail/edggnmnajhcbhlnpjnogkjpghaikidaa
Try doing the following actions, none of them should crash the browser.
1. Tap on an input box, e.g. by going to http://www.google.com.
2. Scrolling a page should work.
3. Go to a page that has no touch handlers, you should be able to scroll the
page w/o problem.
3. Go to a page that has touch handlers (e.g. touchstart), you should be able
to scroll the page w/o problem.
4. Go to a page that has preventDefault() on touchstart event, you shouldn't
be able to scroll the page.

Review URL: https://codereview.chromium.org/572763002

Cr-Commit-Position: refs/heads/master@{#294971}

content/browser/frame_host/render_widget_host_view_guest.cc

@@ -141,12 +141,11 @@ void RenderWidgetHostViewGuest::ProcessAckedTouchEvent(
       INPUT_EVENT_ACK_STATE_CONSUMED) ? ui::ER_HANDLED : ui::ER_UNHANDLED;
   for (ScopedVector<ui::TouchEvent>::iterator iter = events.begin(),
       end = events.end(); iter != end; ++iter)  {
-    if (!ui::GestureRecognizer::Get()->ProcessTouchEventPreDispatch(*(*iter),
-                                                                    this)) {
+    if (!gesture_recognizer_->ProcessTouchEventPreDispatch(*(*iter), this))
       continue;
-    }
+
     scoped_ptr<ui::GestureRecognizer::Gestures> gestures;
-    gestures.reset(ui::GestureRecognizer::Get()->ProcessTouchEventPostDispatch(
+    gestures.reset(gesture_recognizer_->ProcessTouchEventPostDispatch(
         *(*iter), result, this));
     ProcessGestures(gestures.get());
   }