Move source access to a standard location, add chromite to PYTHONPATH.

Rather than having to find /home/${SUDO_USER:-${USER}}/trunk, instead
just look for /mnt/host/trunk (defined by common.sh as $CHROOT_TRUNK_DIR).
This simplifies code flow, and is a requirement for shoving chromite
into PYTHONPATH globally w/in the chroot.

BUG=chromium-os:37347
TEST=cros_sdk --replace; cros_sdk w/ chroot upgrade.
Change-Id: I9ee3e6556541a91193f49cbf74ffc5a8e090537f
Reviewed-on: https://gerrit.chromium.org/gerrit/39921
Tested-by: Brian Harring <ferringb@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
diff --git a/sdk_lib/enter_chroot.sh b/sdk_lib/enter_chroot.sh
index 23078ff..a16da3a 100755
--- a/sdk_lib/enter_chroot.sh
+++ b/sdk_lib/enter_chroot.sh
@@ -86,7 +86,6 @@
 
 INNER_CHROME_ROOT=$FLAGS_chrome_root_mount  # inside chroot
 CHROME_ROOT_CONFIG="/var/cache/chrome_root"  # inside chroot
-INNER_DEPOT_TOOLS_ROOT="/home/${SUDO_USER}/depot_tools"  # inside chroot
 FUSE_DEVICE="/dev/fuse"
 
 chmod 0777 "$FLAGS_chroot/var/lock"
@@ -94,6 +93,11 @@
 LOCKFILE="$FLAGS_chroot/var/lock/enter_chroot"
 MOUNTED_PATH=$(readlink -f "$FLAGS_chroot")
 
+# Reset the depot tools/internal trunk pathways to what they'll
+# be w/in the chroot.
+set_chroot_trunk_dir "${FLAGS_chroot}"
+
+
 setup_mount() {
   # If necessary, mount $source in the host FS at $target inside the
   # chroot directory with $mount_args. We don't write to /etc/mtab because
@@ -213,6 +217,7 @@
         setup_mount /run/shm "--bind" /run/shm
       fi
     fi
+
     setup_mount "${FLAGS_trunk}" "--bind" "${CHROOT_TRUNK_DIR}"
 
     debug "Setting up referenced repositories if required."
@@ -327,7 +332,7 @@
     # A reference to the DEPOT_TOOLS path may be passed in by cros_sdk.
     if [ -n "${DEPOT_TOOLS}" ]; then
       debug "Mounting depot_tools"
-      setup_mount "${DEPOT_TOOLS}" --bind "${INNER_DEPOT_TOOLS_ROOT}"
+      setup_mount "${DEPOT_TOOLS}" --bind "${DEPOT_TOOLS_DIR}"
     fi
 
     # Mount additional directories as specified in .local_mounts file.