Add optional schema compiler error messages

tools/json_schema_compiler/model.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.
 
 import os.path
 
 from json_parse import OrderedDict
 from memoize import memoize
 
 class ParseException(Exception):
@@ skipping 31 matching lines @@
   - |unix_name| the unix_name of the namespace
   - |source_file| the file that contained the namespace definition
   - |source_file_dir| the directory component of |source_file|
   - |source_file_filename| the filename component of |source_file|
   - |platforms| if not None, the list of platforms that the namespace is
                 available to
   - |types| a map of type names to their model.Type
   - |functions| a map of function names to their model.Function
   - |events| a map of event names to their model.Function
   - |properties| a map of property names to their model.Property
-  - |compiler_options| the compiler_options dict, only present if
+  - |compiler_options| the compiler_options dict, only not empty if
                        |include_compiler_options| is True
   """
   def __init__(self, json, source_file, include_compiler_options=False):
     self.name = json['namespace']
     self.unix_name = UnixName(self.name)
     self.source_file = source_file
     self.source_file_dir, self.source_file_filename = os.path.split(source_file)
     self.parent = None
     self.platforms = _GetPlatforms(json)
     toplevel_origin = Origin(from_client=True, from_json=True)
     self.types = _GetTypes(self, json, self, toplevel_origin)
     self.functions = _GetFunctions(self, json, self)
     self.events = _GetEvents(self, json, self)
     self.properties = _GetProperties(self, json, self, toplevel_origin)
-    if include_compiler_options:
-      self.compiler_options = json.get('compiler_options', {})
+    self.compiler_options = (json.get('compiler_options', {})
+        if include_compiler_options else {})
 
 class Origin(object):
   """Stores the possible origin of model object as a pair of bools. These are:
 
   |from_client| indicating that instances can originate from users of
                 generated code (for example, function results), or
   |from_json|   indicating that instances can originate from the JSON (for
                 example, function parameters)
 
   It is possible for model objects to originate from both the client and json,
@@ skipping 389 matching lines @@
 def _GetPlatforms(json):
   if 'platforms' not in json:
     return None
   platforms = []
   for platform_name in json['platforms']:
     for platform_enum in _Enum.GetAll(Platforms):
       if platform_name == platform_enum.name:
         platforms.append(platform_enum)
         break
   return platforms