Touchpad support for laptops
This fix is a workaround to receive mouse wheel and scroll messages
from synaptics touchpad driver used in majority of laptops.
Removed fake scroll bars in RenderWidgetHostHwnd so that it can now
receive mouse wheel messages from synaptics drivers for Dell, Toshiba
Added fake scroll bars to WebContents so that it can receive scroll
messages. WebContents then reflects scroll messages to the view to
give it a chance to handle them.
TEST=Touchpad scrolling and zooming (control + scroll) on various laptops.