Support buttons attribute for drag event (blink side).

Source/core/page/DragController.cpp

Index: Source/core/page/DragController.cpp
diff --git a/Source/core/page/DragController.cpp b/Source/core/page/DragController.cpp
index 054eabfc828fe99260e516de398edafe243d4c38..14fe05f70e2c3c201a452dd1a6c5acfbdeefa34a 100644
--- a/Source/core/page/DragController.cpp
+++ b/Source/core/page/DragController.cpp
@@ -111,15 +111,10 @@ static bool dragTypeIsValid(DragSourceAction action)
 
 static PlatformMouseEvent createMouseEvent(DragData* dragData)
 {
-    int keyState = dragData->modifierKeyState();
-    bool shiftKey = static_cast<bool>(keyState & PlatformEvent::ShiftKey);
-    bool ctrlKey = static_cast<bool>(keyState & PlatformEvent::CtrlKey);
-    bool altKey = static_cast<bool>(keyState & PlatformEvent::AltKey);
-    bool metaKey = static_cast<bool>(keyState & PlatformEvent::MetaKey);
-
     return PlatformMouseEvent(dragData->clientPosition(), dragData->globalPosition(),
-        LeftButton, PlatformEvent::MouseMoved, 0, shiftKey, ctrlKey, altKey,
-        metaKey, PlatformMouseEvent::RealOrIndistinguishable, currentTime());
+        LeftButton, PlatformEvent::MouseMoved, 0,
+        static_cast<PlatformEvent::Modifiers>(dragData->modifierKeyState()),
+        PlatformMouseEvent::RealOrIndistinguishable, currentTime());
 }
 
 static PassRefPtrWillBeRawPtr<DataTransfer> createDraggingDataTransfer(DataTransferAccessPolicy policy, DragData* dragData)