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/util.py

@@ -70,34 +70,3 @@ def hash_file(hash_obj, path):
         break
       hash_obj.update(b)
   return hash_obj
-
-
-def hash_bower_component(hash_obj, path):
-  """Hash the contents of a bower component directory.
-
-  This is a stable hash of a directory downloaded with `bower install`, minus
-  the .bower.json file, which is autogenerated each time by bower. Used in lieu
-  of hashing a zipfile of the contents, since zipfiles are difficult to hash in
-  a stable manner.
-
-  Args:
-    hash_obj: an open hash object, e.g. hashlib.sha1().
-    path: path to the directory to hash.
-
-  Returns:
-    The passed-in hash_obj.
-  """
-  if not os.path.isdir(path):
-    raise ValueError('Not a directory: %s' % path)
-
-  path = os.path.abspath(path)
-  for root, dirs, files in os.walk(path):
-    dirs.sort()
-    for f in sorted(files):
-      if f == '.bower.json':
-        continue
-      p = os.path.join(root, f)
-      hash_obj.update(p[len(path)+1:])
-      hash_file(hash_obj, p)
-
-  return hash_obj