build: Added "uglify-js" as optional compressor

tools/uglify_js.py

@@ -0,0 +1,35 @@
+"""Utility to use the Uglify JS Compiler CLI from Python."""
+
+import logging
+import subprocess
+
+
+def check_available():
+    """ Returns whether the uglify-js tool is available. """
+    subprocess.check_output(['which', 'uglifyjs'])
+
+
+def compile(source_paths, flags=None):
+    """
+    Prepares command-line call to uglify-js compiler.
+
+    Args:
+      source_paths: Source paths to build, in order.
+      flags: A list of additional flags to pass on to uglify-js.
+
+    Returns:
+      The compiled source, as a string, or None if compilation failed.
+    """
+
+    args = ['uglifyjs']
+    args.extend(source_paths)
+    args.extend(['-c', '-m'])
+    if flags:
+        args += flags
+
+    logging.info('Compiling with the following command: %s', ' '.join(args))
+
+    try:
+        return subprocess.check_output(args)
+    except subprocess.CalledProcessError:
+        return