Use correct Ninja arguments in the recipe

Change-Id: I935f591633a19dc7d31905b58b2628ad66f7bb08
diff --git a/infra/recipes/isolate-test.expected/ci.json b/infra/recipes/isolate-test.expected/ci.json
index fdaf5fa..77cea69 100644
--- a/infra/recipes/isolate-test.expected/ci.json
+++ b/infra/recipes/isolate-test.expected/ci.json
@@ -74,6 +74,7 @@
   {
     "cmd": [
       "[START_DIR]/buildtools/ninja",
+      "-C",
       "[START_DIR]/out/Default"
     ],
     "name": "build.build",
diff --git a/infra/recipes/isolate-test.expected/cq_try.json b/infra/recipes/isolate-test.expected/cq_try.json
index e9e6dbe..33cc34b 100644
--- a/infra/recipes/isolate-test.expected/cq_try.json
+++ b/infra/recipes/isolate-test.expected/cq_try.json
@@ -84,6 +84,7 @@
   {
     "cmd": [
       "[START_DIR]/buildtools/ninja",
+      "-C",
       "[START_DIR]/out/Default"
     ],
     "name": "build.build",
diff --git a/infra/recipes/isolate-test.py b/infra/recipes/isolate-test.py
index 22ec426..e45f06f 100644
--- a/infra/recipes/isolate-test.py
+++ b/infra/recipes/isolate-test.py
@@ -47,7 +47,7 @@
         api.step('gen', [buildtools_path.join('gn'), 'gen', out_path,
                          '--root=%s' % api.path['start_dir'],
                          '--dotfile=%s' % api.path['checkout'].join('.gn')])
-        api.step('build', [buildtools_path.join('ninja'), out_path])
+        api.step('build', [buildtools_path.join('ninja'), '-C', out_path])
 
     api.step('test', [out_path.join('host_x64', 'factorial_test')])