Add js_interface_generator for generating extensions interfaces

tools/json_schema_compiler/code.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 class Code(object):
   """A convenience object for constructing code.
 
   Logically each object should be a block of code. All methods except |Render|
   and |IsEmpty| return self.
   """
@@ skipping 11 matching lines @@
     """Appends a line of code at the current indent level or just a newline if
     line is not specified.
 
     substitute: indicated whether this line should be affected by
     code.Substitute().
     new_line: whether this should be added as a new line, or should be appended
         to the last line of the code.
     strip_right: whether or not trailing whitespace should be stripped.
     """
 
-    prefix = indent_level * ' ' if indent_level else ''.join(
+    if line:
+      prefix = indent_level * ' ' if indent_level else ''.join(
         self._line_prefixes)
+    else:
+      prefix = ''
 
     if strip_right:
       line = line.rstrip()
 
     if not new_line and self._code:
       self._code[-1].value += line
     else:
       self._code.append(Line(prefix + line, substitute=substitute))
     return self
 
@@ skipping 131 matching lines @@
     """
     return '\n'.join([l.value for l in self._code])
 
 
 class Line(object):
   """A line of code.
   """
   def __init__(self, value, substitute=True):
     self.value = value
     self.substitute = substitute