Linux installer: Fix APT_SOURCES and APT_SOURCESDIR paths

chrome/installer/linux/common/apt.include

 @@include@@variables.include
 
 APT_GET="`which apt-get 2> /dev/null`"
 APT_CONFIG="`which apt-config 2> /dev/null`"
 
 SOURCES_PREAMBLE="### THIS FILE IS AUTOMATICALLY CONFIGURED ###
 # You may comment out this entry, but any other modifications may be lost.\n"
 
 # Parse apt configuration and return requested variable value.
 apt_config_val() {
@@ skipping 123 matching lines @@
 m5o2ggoONj3qI3JaRHsZaOs1qPQcyd46OyIFUpHJIfk4nezDCoQYd93bWUGqDwxI
 /n/CsdO0365yqDO/ADscehlVqdAupVv2
 =dmoF
 -----END PGP PUBLIC KEY BLOCK-----
 KEYDATA
   fi
 }
 
 # Set variables for the locations of the apt sources lists.
 find_apt_sources() {
+  # NB: These variables only *sometimes* include a trailing slash. (In
+  # particular, in Ubuntu 16.10 / Debian 9, the default value *stopped*
+  # including the trailing slash.) We have to join them with slashes, even
+  # though that sometimes gives a double slash.

[Lei Zhang, 2016/11/08 23:44:35]

Does "${APTDIR%/}/" make it consistently 1 slash?

   APTDIR=$(apt_config_val Dir)
   APTETC=$(apt_config_val 'Dir::Etc')
-  APT_SOURCES="$APTDIR$APTETC$(apt_config_val 'Dir::Etc::sourcelist')"
-  APT_SOURCESDIR="$APTDIR$APTETC$(apt_config_val 'Dir::Etc::sourceparts')"
+  APT_SOURCES="$APTDIR/$APTETC/$(apt_config_val 'Dir::Etc::sourcelist')"
+  APT_SOURCESDIR="$APTDIR/$APTETC/$(apt_config_val 'Dir::Etc::sourceparts')"
 }
 
 # Update the Google repository if it's not set correctly.
 # Note: this doesn't necessarily enable the repository, it just makes sure the
 # correct settings are available in the sources list.
 # Returns:
 # 0 - no update necessary
 # 2 - error
 update_bad_sources() {
   if [ ! "$REPOCONFIG" ]; then
@@ skipping 117 matching lines @@
 get_lib_dir() {
   if [ "$DEFAULT_ARCH" = "i386" ]; then
     LIBDIR=lib/i386-linux-gnu
   elif [ "$DEFAULT_ARCH" = "amd64" ]; then
     LIBDIR=lib/x86_64-linux-gnu
   else
     echo Unknown CPU Architecture: "$DEFAULT_ARCH"
     exit 1
   fi
 }