Merge codereview.chromium.org/630243002 onto 2171 branch

Merge codereview.chromium.org/630243002 onto 2171 branch

Fix extension content verification handling of ./ in icon paths

When extension manifests contain icon paths with a leading ./, we
were failing to process them properly

BUG=410666
Review URL: https://codereview.chromium.org/630243002

Cr-Commit-Position: refs/heads/master@{#298979}
(cherry picked from commit 7cc29ce343a235f9067545ddd19ba2d982c4595f)

Conflicts:
	chrome/browser/extensions/content_verifier_browsertest.cc

Committed: https://chromium.googlesource.com/chromium/src/+/84286ec445962cc0c7feca0eeff96a3155ce17d6

[asargent_no_longer_on_chrome, 2014-10-21 20:31:38]

Committed patchset #1 (id:1) manually as
84286ec445962cc0c7feca0eeff96a3155ce17d6.