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The scroll amount passed into BrowserViewRenderer::ScrollTo is
physical pixel with page_scale_factor applied.
Before --use-zoom-for-dsf enabled, the scroll amount was divided by
both dip_scale_ and page_scale_factor_ to convert to scroll amount
in dip. With the flag enabled, it still need to divide by the
page_scale_factor, but it incorrectly passed the original offset
without take page_scale_factor into account, causes scroll amount
larger than the max_scroll_offset.

When --use-zoom-for-dsf is enabled, scroll_offset_dip_ and
max_scroll_offset_dip_ are convert from/to physical pixel in
every it get used. We shouldn't stored them in dip.

So, this cl changes scroll_offset_dip_ to scroll_offset_unscaled_
and max_scroll_offset_dip_ to max_scroll_offset_unscaled_,
as they were in physical pixel when zoom-for-dsf enabled, and
dip otherwise. Instead of having dip_scale applied every time it
was set.

TEST: webview_ui_test.test.DropDownListTest#testDropDownScaledViewPortUseWideViewPort
Bug: 869995, 873617
Change-Id: I694ca54438620e7afdf8db210704f40fb2c1ba54
Reviewed-on: https://chromium-review.googlesource.com/1162519Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582692}