Remove PlatformEvent it is no longer used.

third_party/WebKit/Source/core/input/MouseEventManager.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/input/MouseEventManager.h"
 
 #include "core/clipboard/DataObject.h"
 #include "core/clipboard/DataTransfer.h"
 #include "core/dom/Element.h"
 #include "core/dom/ElementTraversal.h"
@@ skipping 877 matching lines @@
     return WebInputEventResult::NotHandled;
 
   const bool cancelable = eventType != EventTypeNames::dragleave &&
                           eventType != EventTypeNames::dragend;
 
   IntPoint position = flooredIntPoint(event.positionInRootFrame());
   IntPoint movement = flooredIntPoint(event.movementInRootFrame());
   DragEvent* me = DragEvent::create(
       eventType, true, cancelable, m_frame->document()->domWindow(), 0,
       event.globalX, event.globalY, position.x(), position.y(), movement.x(),
-      movement.y(), static_cast<PlatformEvent::Modifiers>(event.modifiers()), 0,
-      MouseEvent::platformModifiersToButtons(event.modifiers()), nullptr,
+      movement.y(), static_cast<WebInputEvent::Modifiers>(event.modifiers()), 0,
+      MouseEvent::webInputEventModifiersToButtons(event.modifiers()), nullptr,
       TimeTicks::FromSeconds(event.timeStampSeconds()), dataTransfer,
       event.fromTouch() ? MouseEvent::FromTouch
                         : MouseEvent::RealOrIndistinguishable);
 
   return EventHandlingUtil::toWebInputEventResult(
       dragTarget->dispatchEvent(me));
 }
 
 void MouseEventManager::clearDragDataTransfer() {
   if (dragState().m_dragDataTransfer) {
@@ skipping 97 matching lines @@
 
 void MouseEventManager::setClickCount(int clickCount) {
   m_clickCount = clickCount;
 }
 
 bool MouseEventManager::mouseDownMayStartDrag() {
   return m_mouseDownMayStartDrag;
 }
 
 }  // namespace blink