Clean up mb_config.pyl now that we're off GYP.

tools/mb/mb.py

Index: tools/mb/mb.py
diff --git a/tools/mb/mb.py b/tools/mb/mb.py
index b9b11963c05aaa834c10596f099aac51ec3b0531..2a010552e3b6cc2d3b076a8f7c6713652bcb40b5 100755
--- a/tools/mb/mb.py
+++ b/tools/mb/mb.py
@@ -120,6 +120,17 @@ class MetaBuildWrapper(object):
                            'as a JSON object.')
     subp.set_defaults(func=self.CmdAnalyze)
 
+    subp = subps.add_parser('export',
+                            help='print out the expanded configuration for'
+                                 'each builder as a JSON object')
+    subp.add_argument('-f', '--config-file', metavar='PATH',
+                      default=self.default_config,
+                      help='path to config file '
+                          '(default is //tools/mb/mb_config.pyl)')
+    subp.add_argument('-g', '--goma-dir',
+                      help='path to goma directory')
+    subp.set_defaults(func=self.CmdExport)
+
     subp = subps.add_parser('gen',
                             help='generate a new set of build files')
     AddCommonOptions(subp)
@@ -249,6 +260,33 @@ class MetaBuildWrapper(object):
     else:
       return self.RunGYPAnalyze(vals)
 
+  def CmdExport(self):
+    self.ReadConfigFile()
+    obj = {}
+    for master, builders in self.masters.items():
+      obj[master] = {}
+      for builder in builders:
+        config = self.masters[master][builder]
+        if not config:
+          continue
+
+        if isinstance(config, list):
+          args = [self.FlattenConfig(c)['gn_args'] for c in config]
+        elif config.startswith('//'):
+          args = config
+        else:
+          args = self.FlattenConfig(config)['gn_args']
+          if 'error' in args:
+            continue
+
+        obj[master][builder] = args
+
+    # Dump object and trim trailing whitespace.
+    s = '\n'.join(l.rstrip() for l in
+                  json.dumps(obj, sort_keys=True, indent=2).splitlines())
+    self.Print(s)
+    return 0
+
   def CmdGen(self):
     vals = self.Lookup()
     self.ClobberIfNeeded(vals)
@@ -598,7 +636,8 @@ class MetaBuildWrapper(object):
 
     # Do some basic sanity checking on the config so that we
     # don't have to do this in every caller.
-    assert 'type' in vals, 'No meta-build type specified in the config'
+    if 'type' not in vals:
+        vals['type'] = 'gn'
     assert vals['type'] in ('gn', 'gyp'), (
         'Unknown meta-build type "%s"' % vals['gn_args'])
 
@@ -688,7 +727,7 @@ class MetaBuildWrapper(object):
     vals = {
       'args_file': '',
       'cros_passthrough': False,
-      'gn_args': [],
+      'gn_args': '',
       'gyp_defines': '',
       'gyp_crosscompile': False,
       'type': None,