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
diff --git a/url/url_constants.cc b/url/url_constants.cc
index 7eac6587..d5c57f4 100644
--- a/url/url_constants.cc
+++ b/url/url_constants.cc
@@ -6,6 +6,9 @@
 
 namespace url {
 
+const char kAboutBlankURL[] = "about:blank";
+
+const char kAboutScheme[] = "about";
 const char kBlobScheme[] = "blob";
 const char kDataScheme[] = "data";
 const char kFileScheme[] = "file";