Add isolate for content_browsertests with --site-per-process.

tools/mb/mb.py

Index: tools/mb/mb.py
diff --git a/tools/mb/mb.py b/tools/mb/mb.py
index 3ec07230368b8fe9b81fcb6303e632c15f106c06..abf7beff061143361237373e4a1841d29be4cc45 100755
--- a/tools/mb/mb.py
+++ b/tools/mb/mb.py
@@ -535,7 +535,8 @@ class MetaBuildWrapper(object):
     for target in swarming_targets:
       if gn_isolate_map[target]['type'] == 'gpu_browser_test':
         runtime_deps_target = 'browser_tests'
-      elif gn_isolate_map[target]['type'] == 'script':
+      elif (gn_isolate_map[target]['type'] == 'script' or
+            gn_isolate_map[target].get('label_type') == 'group'):
         # For script targets, the build target is usually a group,
         # for which gn generates the runtime_deps next to the stamp file
         # for the label, which lives under the obj/ directory.
@@ -733,17 +734,19 @@ class MetaBuildWrapper(object):
       cmdline = [
           '../../testing/test_env.py',
           '../../' + self.ToSrcRelPath(gn_isolate_map[target]['script'])
-      ] + gn_isolate_map[target].get('args', [])
+      ]
     elif test_type in ('raw'):
       extra_files = []
       cmdline = [
           './' + str(target) + executable_suffix,
-      ] + gn_isolate_map[target].get('args')
+      ]
 
     else:
       self.WriteFailureAndRaise('No command line for %s found (test type %s).'
                                 % (target, test_type), output_path=None)
 
+    cmdline += gn_isolate_map[target].get('args', [])
+
     return cmdline, extra_files
 
   def ToAbsPath(self, build_path, *comps):