Added a function to update chroot sudoers automatically.

This function is now called by enter_chroot.sh.  A separate change
will call the function from make_chroot

Change-Id: I4fc07c413e56db3e5e7617428f20f2ffc02790d7

BUG=chromium-os:7072
TEST=Took root out of sudoers and ran enter_chroot.sh script; saw that it was re-added.

Review URL: http://codereview.chromium.org/3909001

common.sh

@@ -460,3 +460,23 @@ print_time_elapsed() {
   seconds="$(( $elapsed_seconds % 60 ))"
   echo "Elapsed time: ${minutes}m${seconds}s"
 }
+
+# This function is a place to put code to incrementally update the
+# chroot so that users don't need to fully re-make it.  It should
+# be called from scripts that are run _outside_ the chroot.
+#
+# Please put date information so it's easy to keep track of when
+# old hacks can be retired and so that people can detect when a
+# hack triggered when it shouldn't have.
+#
+# ${1} specifies the location of the chroot.
+chroot_hacks_from_outside() {
+  # Give args better names.
+  local chroot_dir="${1}"
+
+  # Add root as a sudoer if not already done.
+  if ! sudo grep -q '^root ALL=(ALL) ALL$' "${chroot_dir}/etc/sudoers" ; then
+    info "Upgrading old chroot (pre 2010-10-19) - adding root to sudoers"
+    sudo bash -c "echo root ALL=\(ALL\) ALL >> \"${chroot_dir}/etc/sudoers\""
+  fi
+}

enter_chroot.sh

@@ -254,6 +254,10 @@ then
   exit 0
 fi
 
+# Apply any hacks needed to update the chroot.
+chroot_hacks_from_outside "${FLAGS_chroot}"
+
+
 # Make sure we unmount before exiting
 trap teardown_env EXIT
 setup_env