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Fail back to shortcut if there is no enough space to install WebApk even after
freeing cache.

Free cache and install if there is no enough space but the space requirement
can be satisfied using the cache storage.

Bug: 774513,736457
Change-Id: I1beec2b3c26ebfb09e03014038a2657b27185284
Reviewed-on: https://chromium-review.googlesource.com/794532Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Peter Kotwicz <pkotwicz@chromium.org>
Commit-Queue: Ran Ji <ranj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525321}