Fix potential crash in FrameView::setScrollOffset
Fix potential crash in FrameView::setScrollOffset

There was a code path that was checking if layoutView was non-null yet
there was a code path that used it unconditionally. The unconditional
path seems to match a crash stack. Move the clearHitTestCache
code path into the conditional.

BUG=611683

Review-Url: https://codereview.chromium.org/2004503003
Cr-Commit-Position: refs/heads/master@{#395260}
(cherry picked from commit 715aea1e3a3cd8a91f43390ec4f2166df3753a11)

Review URL: https://codereview.chromium.org/2010513002 .

Cr-Commit-Position: 03d981dee550804c6934fd1a1d9cfa3c172affd3@{#29}
Cr-Branched-From: e9621a186760eb36d74098d9e33e4dd91c427b34@{#394939}

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