Fill the modifier state for scroll on Touchpad

Since touchpad gestures will expose as mousewheel events on JS.
Developer may want the modifier state. In this patch, we read the
modifier state and fill it into the event.

Bug: 779372
Change-Id: Idf3ab53433795a40c7e89c887a9bb38a0c9f5f6b
Reviewed-on: https://chromium-review.googlesource.com/996379Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548824}

ui/views/win/hwnd_message_handler.cc

@@ -1118,15 +1118,17 @@ void HWNDMessageHandler::ApplyPanGestureEvent(
   gfx::Point cursor_location(location);
   gfx::Point cursor_root_location(root_location);
 
+  int modifiers = ui::GetModifiersFromKeyState();
+
   if (IsPrecisionTouchpadNavigationGestureEnabled()) {
     ui::ScrollEvent event(ui::ET_SCROLL, cursor_location, ui::EventTimeForNow(),
-                          ui::EF_NONE, scroll_x, scroll_y, scroll_x, scroll_y,
-                          2, momentum_phase, phase);
+                          modifiers, scroll_x, scroll_y, scroll_x, scroll_y, 2,
+                          momentum_phase, phase);
     delegate_->HandleScrollEvent(&event);
   } else {
     ui::MouseWheelEvent wheel_event(
         offset, cursor_location, cursor_root_location, base::TimeTicks::Now(),
-        ui::EF_PRECISION_SCROLLING_DELTA, ui::EF_NONE);
+        modifiers | ui::EF_PRECISION_SCROLLING_DELTA, ui::EF_NONE);
     delegate_->HandleMouseEvent(&wheel_event);
   }
 }