Use ninja as the default GYP generator on FreeBSD.

build/gyp_chromium

Index: build/gyp_chromium
diff --git a/build/gyp_chromium b/build/gyp_chromium
index e8e069bc84985c2cf383643d0759d821a007f45a..5ada9897efaed921a6dde70a217356e54f862555 100755
--- a/build/gyp_chromium
+++ b/build/gyp_chromium
@@ -524,9 +524,8 @@ if __name__ == '__main__':
   # . -f / --format has precedence over the env var, no need to check for it
   # . set the env var only if it hasn't been set yet
   # . chromium.gyp_env has been applied to os.environ at this point already
-  if sys.platform.startswith('linux') and not os.environ.get('GYP_GENERATORS'):
-    os.environ['GYP_GENERATORS'] = 'ninja'
-  if sys.platform.startswith('win') and not os.environ.get('GYP_GENERATORS'):
+  if sys.platform.startswith(('linux', 'win', 'freebsd')) and \
+      not os.environ.get('GYP_GENERATORS'):
     os.environ['GYP_GENERATORS'] = 'ninja'
   elif sys.platform == 'darwin' and not os.environ.get('GYP_GENERATORS') and \
       not 'OS=ios' in os.environ.get('GYP_DEFINES', []):