Make MB aware of iOS bot configs and get iOS working.

tools/mb/mb.py

Index: tools/mb/mb.py
diff --git a/tools/mb/mb.py b/tools/mb/mb.py
index c3be5d7fdff88df36051b9adacdf8e160055c9c9..36fa8789fe8ad48b96b608ab7bfa4737f62d1466 100755
--- a/tools/mb/mb.py
+++ b/tools/mb/mb.py
@@ -355,9 +355,37 @@ 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'
-    assert vals['type'] in ('gn', 'gyp'), (
+    assert vals['type'] in ('gn', 'gyp', 'passthrough'), (
         'Unknown meta-build type "%s"' % vals['gn_args'])
 
+    if vals['type'] == 'passthrough':
+      vals = self.HandlePassthrough()
+
+    return vals
+
+  def HandlePassthrough(self):
+    if 'MB_TYPE' not in os.environ:
+      raise MBErr('MB_TYPE not set in the environment')
+    mb_type = os.environ['MB_TYPE']
+    if mb_type not in ('gyp', 'gn'):
+      raise MBErr('illegal value "%s" for MB_TYPE', mb_type)
+
+    vals = self.DefaultConfigVals()
+    vals['type'] = mb_type
+    if mb_type == 'gyp':
+      if 'GYP_CROSSCOMPILE' in os.environ:
+        if os.environ['GYP_CROSSCOMPILE'] == '1':
+          vals['gyp_crosscompile'] = True
+      if 'GYP_DEFINES' not in os.environ:
+        raise MBErr('GYP_DEFINES not set in environment on a '
+                    'passthrough bot set to type GYP.')
+      vals['gyp_defines'] = os.environ['GYP_DEFINES']
+    else:
+      if 'gn_args' not in os.environ:
+        raise MBErr('GN_ARGS not set in environment on a passthrough bot'
+                    ' set to type GN')
+      vals['gn_args'] = os.environ.get('GN_ARGS', '')
+
     return vals
 
   def ReadConfigFile(self):
@@ -401,17 +429,19 @@ class MetaBuildWrapper(object):
 
   def FlattenConfig(self, config):
     mixins = self.configs[config]
-    vals = {
+    vals = self.DefaultConfigVals()
+    visited = []
+    self.FlattenMixins(mixins, vals, visited)
+    return vals
+
+  def DefaultConfigVals(self):
+    return {
       'type': None,
       'gn_args': [],
       'gyp_defines': '',
       'gyp_crosscompile': False,
     }
 
-    visited = []
-    self.FlattenMixins(mixins, vals, visited)
-    return vals
-
   def FlattenMixins(self, mixins, vals, visited):
     for m in mixins:
       if m not in self.mixins: