GitLab

Design: go/chrome-fallback-icons

This adds FallbackIconUrlParser, which will be used to parse the
"explict flow" host chrome://fallback-icon/ to extract size,
FallbackIconStyle, and URL needed to render Fallback icons.

This CL is sliced off from https://codereview.chromium.org/835903005/ .

BUG=455063

Review URL: https://codereview.chromium.org/924063003

Cr-Commit-Position: refs/heads/master@{#318771}