Use GN in simple chrome builders

BUG=605154

Review URL: https://codereview.chromium.org/1918713005

Cr-Commit-Position: refs/heads/master@{#389914}

tools/mb/mb_config.pyl

@@ -66,9 +66,9 @@
     },
 
     'chromium.chromiumos': {
-      'ChromiumOS amd64-generic Compile': 'cros_chrome_sdk_gyp',
-      'ChromiumOS daisy Compile': 'cros_chrome_sdk_gyp',
-      'ChromiumOS x86-generic Compile': 'cros_chrome_sdk_gyp',
+      'ChromiumOS amd64-generic Compile': 'cros_chrome_sdk_gn',
+      'ChromiumOS daisy Compile': 'cros_chrome_sdk_gn',
+      'ChromiumOS x86-generic Compile': 'cros_chrome_sdk_gn',
       'Linux ChromiumOS Builder': 'swarming_chromeos_gyp_release_bot',
       'Linux ChromiumOS Builder (dbg)': 'swarming_chromeos_gyp_debug_bot',
       'Linux ChromiumOS Full': 'swarming_chromeos_gyp_release_bot',
@@ -1061,6 +1061,9 @@
     'cros_chrome_sdk_gyp': [
       'gyp', 'cros_chrome_sdk',
     ],
+    'cros_chrome_sdk_gn': [
+      'gn', 'cros_chrome_sdk',
+    ],
 
     # The 'findit' config is used by the *_variable_* bots, which run
     # the 'FindIt' recipes and code to bisect failures that happen on the