GitLab

In Widget::OnMouseEvent(), do not handle MOUSE_MOVED
events as MOUSE_DRAGGED events, and do not handle
MOUSE_DRAGGED events as MOUSE_MOVED events; instead
trust that the mouse event type has been set correctly
before arriving at Widget. This also allows us to
remove the member |is_mouse_button_pressed_|
from Widget.

BUG=412929, 412931
TEST=WidgetTest.DragIntoView, WidgetTest.DragOutOfView

Review URL: https://codereview.chromium.org/560053002

Cr-Commit-Position: refs/heads/master@{#297215}