Add GN (the build tool) to the chromium.linux buildbots and try jobs

scripts/slave/recipe_modules/chromium/api.py

Index: scripts/slave/recipe_modules/chromium/api.py
diff --git a/scripts/slave/recipe_modules/chromium/api.py b/scripts/slave/recipe_modules/chromium/api.py
index 46eae8bc24fc672331fd22b1d169ca7d6100ddfa..2c8ecfe3fdae6a6e46010b881c21e25316a2e6e3 100644
--- a/scripts/slave/recipe_modules/chromium/api.py
+++ b/scripts/slave/recipe_modules/chromium/api.py
@@ -230,13 +230,31 @@ class ChromiumApi(recipe_api.RecipeApi):
         python_mode=True,
         xvfb=True)
 
-  def runhooks(self, **kwargs):
+  def runhooks(self, run_gyp=True, **kwargs):
     """Run the build-configuration hooks for chromium."""
     env = kwargs.get('env', {})
-    env.update(self.c.gyp_env.as_jsonish())
+    if run_gyp:
+      env.update(self.c.gyp_env.as_jsonish())
+    else:
+      env['GYP_CHROMIUM_NO_ACTION'] = 1
     kwargs['env'] = env
     return self.m.gclient.runhooks(**kwargs)
 
+  def compile_with_ninja(self, name, output_dir):
+    ninja_path = self.m.path['depot_tools'].join('ninja',
+                                                 platform_ext={'win': '.exe'})
+    return self.m.step(name=name, cmd=[ninja_path, '-C', output_dir])
+
+  def run_gn(self, output_dir):
+    config = self.c.BUILD_CONFIG
+    gn_wrapper_script_path = self.m.path['depot_tools'].join('gn.py')
+    gn_build_config_specific_args = {
+        'Debug': ['--args=is_debug=true'],
+        'Release': ['--args=is_debug=false'],
+    }
+    gn_args = ['gen', '-o', output_dir] + gn_build_config_specific_args[config]
+    return self.m.python('gn', gn_wrapper_script_path, args=gn_args)
+
   def taskkill(self):
     return self.m.python(
       'taskkill',