Made RenderBox::scrollRectToVisible pinch viewport aware.

Made the visible rect correspond to the actual visible area viewable
through the pinch viewport. The scrolling now takes into account
the pinch viewport so if the given rect can't be scrolled into view
via scrolling the main FrameView, the PinchViewport is scrolled so
that it does.

This fixes "Find In Page" to scroll matches into view while the ChromeOS
keyboard is up or when the page is pinch-zoomed in. It also fixes
autoscroll while pinch-zoomed in.

BUG=369321

Review URL: https://codereview.chromium.org/299363006

git-svn-id: svn://svn.chromium.org/blink/trunk@175301 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Enable zero length source size in sizes attribute

According to the spec, zero-length source-size is permitted.
For some reason, current implementation treats them as invalid.
This CL fixes that.

BUG=379088

Review URL: https://codereview.chromium.org/302123002

git-svn-id: svn://svn.chromium.org/blink/trunk@175302 bbb929c8-8fbe-4397-9dbb-9b2b20218538