GitLab

Making ParsedFallbackIconPath resemble ParsedFaviconPath, to prepare it
for chrome-search:// URL with <view_id>/<restricted_id> . Details:
- Replacing url() with url_string(). Need to update chrome://large-icon
  endpoint and test to accommodate.
- Adding path_index().

BUG=467712

Review URL: https://codereview.chromium.org/1017803003

Cr-Commit-Position: refs/heads/master@{#321615}