Add unsupported option to install-build-deps.

Add an option --unsupported to install-build-deps.sh which allows the
installation to be attempted on a system we don't support. Omit
mentioning this in the error, in the hope that anyone who can deal with
the fallout from this will find it in the script. Also, add GCEL
(Ubuntu-derived image used by Compute Engine) to the list of supported
systems.

BUG=

Review URL: https://codereview.chromium.org/11863012

git-svn-id: http://src.chromium.org/svn/trunk/src/build@176982 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

install-build-deps.sh

@@ -31,6 +31,7 @@ do
   --no-prompt)              do_default=1
                             do_quietly="-qq --assume-yes"
     ;;
+  --unsupported)            do_unsupported=1;;
   *) usage;;
   esac
   shift
@@ -38,10 +39,16 @@ done
 
 ubuntu_versions="10\.04|10\.10|11\.04|11\.10|12\.04|12\.10"
 ubuntu_codenames="lucid|maverick|natty|oneiric|precise|quantal"
+ubuntu_issue="Ubuntu ($ubuntu_versions|$ubuntu_codenames)"
+# GCEL is an Ubuntu-derived VM image used on Google Compute Engine; /etc/issue
+# doesn't contain a version number so just trust that the user knows what
+# they're doing.
+gcel_issue="^GCEL"
 
-if ! egrep -q "Ubuntu ($ubuntu_versions|$ubuntu_codenames)" /etc/issue; then
-  echo "ERROR: Only Ubuntu 10.04 (lucid) through 12.10 (quantal) are currently"\
-      "supported" >&2
+if [ 0 -eq "${do_unsupported-0}" ] ; then
+  if ! egrep -q "($ubuntu_issue|$gcel_issue)" /etc/issue; then
+    echo "ERROR: Only Ubuntu 10.04 (lucid) through 12.10 (quantal) are"\
+        "currently supported" >&2
     exit 1
   fi
 
@@ -49,6 +56,7 @@ if ! uname -m | egrep -q "i686|x86_64"; then
     echo "Only x86 architectures are currently supported" >&2
     exit
   fi
+fi
 
 if [ "x$(id -u)" != x0 ]; then
   echo "Running as non-root user."