Add support for building targets directly from gyp.

pylib/gyp/__init__.py

Index: pylib/gyp/__init__.py
diff --git a/pylib/gyp/__init__.py b/pylib/gyp/__init__.py
index ba1ca07ba51a6636adcb20036cd06e731a2f6cf4..96290fad78466e2b1e293bb90fc69a74e020e164 100755
--- a/pylib/gyp/__init__.py
+++ b/pylib/gyp/__init__.py
@@ -314,6 +314,8 @@ def gyp_main(args):
   parser.add_option('--toplevel-dir', dest='toplevel_dir', action='store',
                     default=None, metavar='DIR', type='path',
                     help='directory to use as the root of the source tree')
+  parser.add_option('--build', dest='configs', action='append',
+                    help='configuration for build after project generation')
   # --no-circular-check disables the check for circular relationships between
   # .gyp files.  These relationships should not exist, but they've only been
   # observed to be harmful with the Xcode generator.  Chromium's .gyp files
@@ -496,6 +498,13 @@ def gyp_main(args):
     # generate targets in the order specified in flat_list.
     generator.GenerateOutput(flat_list, targets, data, params)
 
+    if options.configs:
+      valid_configs = targets[flat_list[0]]['configurations'].keys()
+      for conf in options.configs:
+        if conf not in valid_configs:
+          raise GypError('Invalid config specified via --build: %s' % conf)
+      generator.PerformBuild(data, options.configs, params)
+
   # Done
   return 0