Fire visualviewportchanged event on window rather than document

In https://codereview.chromium.org/2025393003/ I moved the visualViewport object
from document onto window but forgot to move the event to fire on the window
instead.

BUG=595826

Review-Url: https://codereview.chromium.org/2034313002
Cr-Commit-Position: refs/heads/master@{#398067}

third_party/WebKit/LayoutTests/fast/dom/viewport/visualviewportchanged-event-fired-window-resized.html

@@ -19,7 +19,7 @@
         // Turn off smooth scrolling.
         internals.settings.setScrollAnimatorEnabled(false);
 
-        document.addEventListener('visualviewportchanged', function(e) {
+        window.addEventListener('visualviewportchanged', function(e) {
             numCalls++;
         });
 

third_party/WebKit/LayoutTests/fast/dom/viewport/visualviewportchanged-event-fired.html

@@ -35,7 +35,7 @@
         // Turn off smooth scrolling.
         internals.settings.setScrollAnimatorEnabled(false);
 
-        document.addEventListener('visualviewportchanged', function(e) {
+        window.addEventListener('visualviewportchanged', function(e) {
             numCalls++;
         });
 

third_party/WebKit/Source/core/dom/Document.cpp

@@ -3928,7 +3928,7 @@ void Document::enqueueMediaQueryChangeListeners(HeapVector<Member<MediaQueryList
 void Document::enqueueVisualViewportChangedEvent()
 {
     Event* event = Event::create(EventTypeNames::visualviewportchanged);
-    event->setTarget(this);
+    event->setTarget(domWindow());
     ensureScriptedAnimationController().enqueuePerFrameEvent(event);
 }