Use changed_button_flags() when converting MouseEvent to blink::WebMouseEvent.
Event::flags() contains all the buttons that are being held down during event,
while MouseEvent::changed_button_flags() contains the buttons that are
actually pressed/released during the press/release event (and this is what we
really are interested in).
This is a follow up to https://codereview.chromium.org/302593002/ which caused problems
during integration, and it seems to me it got just closed, so I am opening a new one.
Review URL: https://codereview.chromium.org/585393002
Cr-Commit-Position: refs/heads/master@{#296691}
1 file changed
