Revert of Remove the 'gyp_config' concept from MB.

tools/mb/mb_unittest.py

Index: tools/mb/mb_unittest.py
diff --git a/tools/mb/mb_unittest.py b/tools/mb/mb_unittest.py
index a6f2789f59777995d10234700d30e64f842f2188..8c76e5048bed8c724a438957f587afea9cd49d26 100755
--- a/tools/mb/mb_unittest.py
+++ b/tools/mb/mb_unittest.py
@@ -121,9 +121,11 @@
     },
     'rel': {
       'gn_args': 'is_debug=false',
+      'gyp_config': 'Release',
     },
     'debug': {
       'gn_args': 'is_debug=true',
+      'gyp_config': 'Debug',
     },
   },
   'private_configs': ['private'],
@@ -302,7 +304,7 @@
   def test_gyp_lookup_goma_dir_expansion(self):
     self.check(['lookup', '-c', 'gyp_rel_bot', '-g', '/foo'], ret=0,
                out=("python build/gyp_chromium -G 'output_dir=<path>' "
-                    "-D goma=1 -D gomadir=/foo\n"))
+                    "-G config=Release -D goma=1 -D gomadir=/foo\n"))
 
   def test_help(self):
     orig_stdout = sys.stdout