Speculative ShelfView::GetTitleForView crash fix.
Speculative ShelfView::GetTitleForView crash fix.

Return empty string if any needed values are null.

BUG=612042
TEST=No crash repro (I can't repro with or without this CL...)
R=jamescook@chromium.org,sky@chromium.org

Review-Url: https://codereview.chromium.org/1994253004
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#394896}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk