Implement multi-phase build support in MB.

tools/mb/mb.py

Index: tools/mb/mb.py
diff --git a/tools/mb/mb.py b/tools/mb/mb.py
index 3ee71030d0086462afe125bf4064fb3a4a160b00..c21e2f10879f11ee85bc4d03fac9fbd5cfc35a13 100755
--- a/tools/mb/mb.py
+++ b/tools/mb/mb.py
@@ -78,6 +78,9 @@ class MetaBuildWrapper(object):
                         help='master name to look up config from')
       subp.add_argument('-c', '--config',
                         help='configuration to analyze')
+      subp.add_argument('--phase', type=int,
+                        help=('build phase for a given build '
+                              '(int in [1, 2, ...))'))
       subp.add_argument('-f', '--config-file', metavar='PATH',
                         default=self.default_config,
                         help='path to config file '
@@ -328,7 +331,11 @@ class MetaBuildWrapper(object):
     all_configs = {}
     for master in self.masters:
       for config in self.masters[master].values():
-        all_configs[config] = master
+        if isinstance(config, list):
+          for c in config:
+            all_configs[c] = master
+        else:
+          all_configs[config] = master
 
     # Check that every referenced args file or config actually exists.
     for config, loc in all_configs.items():
@@ -475,10 +482,15 @@ class MetaBuildWrapper(object):
         config = self.masters[master][builder]
         if config == 'tbd':
           tbd.add(builder)
+        elif isinstance(config, list):
+          vals = self.FlattenConfig(config[0])
+          if vals['type'] == 'gyp':
+            gyp.add(builder)
+          else:
+            done.add(builder)
         elif config.startswith('//'):
           done.add(builder)
         else:
-          # TODO(dpranke): Check if MB is actually running?
           vals = self.FlattenConfig(config)
           if vals['type'] == 'gyp':
             gyp.add(builder)
@@ -522,12 +534,6 @@ class MetaBuildWrapper(object):
         self.RunGNGen(vals)
       return vals
 
-    # TODO: We can only get the config for GN build dirs, not GYP build dirs.
-    # GN stores the args that were used in args.gn in the build dir,
-    # but GYP doesn't store them anywhere. We should consider modifying
-    # gyp_chromium to record the arguments it runs with in a similar
-    # manner.
-
     mb_type_path = self.PathJoin(self.ToAbsPath(build_dir), 'mb_type')
     if not self.Exists(mb_type_path):
       toolchain_path = self.PathJoin(self.ToAbsPath(build_dir),
@@ -656,12 +662,24 @@ class MetaBuildWrapper(object):
       raise MBErr('Builder name "%s"  not found under masters[%s] in "%s"' %
                   (self.args.builder, self.args.master, self.args.config_file))
 
-    return self.masters[self.args.master][self.args.builder]
+    config = self.masters[self.args.master][self.args.builder]
+    if isinstance(config, list):
+      if self.args.phase is None:
+        raise MBErr('Must specify a build --phase for %s on %s' %
+                    (self.args.builder, self.args.master))
+      phase = int(self.args.phase)
+      if phase < 1 or phase > len(config):
+        raise MBErr('Phase %d out of bounds for %s on %s' %
+                    (phase, self.args.builder, self.args.master))
+      return config[phase-1]
+
+    if self.args.phase is not None:
+      raise MBErr('Must not specify a build --phase for %s on %s' %
+                  (self.args.builder, self.args.master))
+    return config
 
   def FlattenConfig(self, config):
     mixins = self.configs[config]
-    # TODO(dpranke): We really should provide a constructor for the
-    # default set of values.
     vals = {
       'args_file': '',
       'cros_passthrough': False,
@@ -680,8 +698,6 @@ class MetaBuildWrapper(object):
       if m not in self.mixins:
         raise MBErr('Unknown mixin "%s"' % m)
 
-      # TODO: check for cycles in mixins.
-
       visited.append(m)
 
       mixin_vals = self.mixins[m]
@@ -976,7 +992,6 @@ class MetaBuildWrapper(object):
 
     # This needs to mirror the settings in //build/config/ui.gni:
     # use_x11 = is_linux && !use_ozone.
-    # TODO(dpranke): Figure out how to keep this in sync better.
     use_x11 = (self.platform == 'linux2' and
                not android and
                not 'use_ozone=true' in vals['gn_args'])