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Obtain the inner viewport origin, touch and target rectangles
from the Blink relative to the outer viewport.
Use the zoom rectangle in the outer viewport coordinates for bitmap
generation but the inner viewport coordinates for the calculation
of the physical window zoom rect.

This change is part 2 of 2 (part 1 is Blink side change https://codereview.chromium.org/584893004).

BUG=370470

Review URL: https://codereview.chromium.org/595693002

Cr-Commit-Position: refs/heads/master@{#296786}