Merge branch ambrop72/chromium-update.

Upgrades and fixes the build of the current Chromium stable channel.

 * Update versions.
 * Use gyp package not gyp_svn1977.
 * Remove icu from buildInputs, since this causes a build error due to
   inferference with use_system_icu=false.
 * Remove the hack that inserts the absolute path into gyp files, and
   pass --depth . to gyp. This resolves the third_party/angle gyp error.
 * Do a normal copy of the source code not a symlink copy. This resolves
   some link error where the symlinks interfere with relative paths
   (seems like because gyp resolves symlinks first). Note, this used to
   be worked around with the absolute path insertion hack.
 * Change the bucketURL in update.nix to https (for more secure
   updates).