bazel: bower support

* npm_binary (download tarball packaged npm apps)

* bower_archive (download a zip file, to be put in WORKSPACE)

* bower_component (defining a bower library, with dependency )

* bower_component_bundle (zipping up libraries together)

* js_component (insert plain js file into bower component bundle)

* bower2bazel.py: run bower to find dependencies, generate a .bzl to
  define archives and define components

Tested:

 python tools/js/bower2bazel.py -w lib/js/bower_archives.bzl -b \
    lib/js/bower_components.bzl

 bazel build polygerrit-ui:components
 unzip -v bazel-bin/polygerrit-ui/components.zip > /tmp/baz

 buck build polygerrit-ui:polygerrit_components
 unzip -v buck-out/gen/polygerrit-ui/polygerrit_components/polygerrit_components.bower_components.zip > /tmp/buck

 diff /tmp/buck /tmp/baz

The diff corresponds to newer file versions pinned through bower2bazel.

Change-Id: I4f33914d4853bcf8afe78b4719d0e0e83b139031

tools/js/run_npm_binary.py

@@ -25,8 +25,6 @@ import sys
 import tarfile
 import tempfile
 
-from tools import util
-
 
 def extract(path, outdir, bin):
   if os.path.exists(os.path.join(outdir, bin)):
@@ -59,19 +57,21 @@ def extract(path, outdir, bin):
     # finished.
     extract_one(tar.getmember(bin))
 
-
 def main(args):
   path = args[0]
   suffix = '.npm_binary.tgz'
   tgz = os.path.basename(path)
+
   parts = tgz[:-len(suffix)].split('@')
 
   if not tgz.endswith(suffix) or len(parts) != 2:
     print('usage: %s <path/to/npm_binary>' % sys.argv[0], file=sys.stderr)
     return 1
 
-  name, version = parts
-  sha1 = util.hash_file(hashlib.sha1(), path).hexdigest()
+  name, _ = parts
+
+  # Avoid importing from gerrit because we don't want to depend on the right CWD.
+  sha1 = hashlib.sha1(open(path, 'rb').read()).hexdigest()
   outdir = '%s-%s' % (path[:-len(suffix)], sha1)
   rel_bin = os.path.join('package', 'bin', name)
   bin = os.path.join(outdir, rel_bin)