V8: Let peek-gn use mb to reuse v8-side configs.

scripts/slave/recipe_modules/v8/api.py

Index: scripts/slave/recipe_modules/v8/api.py
diff --git a/scripts/slave/recipe_modules/v8/api.py b/scripts/slave/recipe_modules/v8/api.py
index 2dc5b9e151b433e48e30ae1d0536746e3fd2a15a..3058001dc8d9287557ea46ea1e6a54e56d411f06 100644
--- a/scripts/slave/recipe_modules/v8/api.py
+++ b/scripts/slave/recipe_modules/v8/api.py
@@ -277,8 +277,27 @@ class V8Api(recipe_api.RecipeApi):
     gyp_build_dir = self.m.chromium.c.build_dir.join(
         self.m.chromium.c.build_config_fs)
     with self.m.tempfile.temp_dir('v8_gn') as gn_build_dir:
-      self.m.chromium.run_gn(
-          use_goma=True, build_dir=gn_build_dir, ok_ret='any')
+      step_result = self.m.python(
+          name='patch mb config (fyi)',
+          script=self.resource('patch_mb_config.py'),
+          args=[
+            self.m.path['checkout'].join('infra', 'mb', 'mb_config.pyl'),
+            self.m.raw_io.output(),
+          ],
+          step_test_data=lambda: self.m.raw_io.test_api.output('[mb config]'),
+          ok_ret='any',
+      )
+      use_goma = (self.m.chromium.c.compile_py.compiler and
+                  'goma' in self.m.chromium.c.compile_py.compiler)
+      self.m.chromium.run_mb(
+          self.m.properties['mastername'],
+          self.m.properties['buildername'],
+          name='generate_build_files with gn (fyi)',
+          use_goma=use_goma,
+          mb_config_path=self.m.raw_io.input(step_result.raw_io.output),
+          build_dir=gn_build_dir,
+          ok_ret='any',
+      )
       self.m.python(
           'compare build flags (fyi)',
           self.m.path['checkout'].join('tools', 'gyp_flag_compare.py'),