Windows: Fix crash by starting pan-scrolling when render tree needs to be updated.

It's possible that RenderBox::canBeScrolledAndHasScrollableArea()
modifies render tree and the |while| loop in Node::defaultEventHandler
is confused. We should make sure render tree is up-to-date before the
loop.

BUG=401362

Review URL: https://codereview.chromium.org/471373002

git-svn-id: svn://svn.chromium.org/blink/trunk@180539 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Give BitmapImage::draw "bm" a name

Abbrvs are not our style, call it an image.

BUG=None

Review URL: https://codereview.chromium.org/481373002

git-svn-id: svn://svn.chromium.org/blink/trunk@180540 bbb929c8-8fbe-4397-9dbb-9b2b20218538