Move about://-related constants from //content to //url

kAboutScheme and kAboutBlankURL are used in code shared by iOS, and are general
enough to live in //url instead of //content.

TBR=yoz,benm

Review URL: https://codereview.chromium.org/325443002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275988 0039d316-1c4b-4281-b951-d872f2087c98
100 files changed