I think that only ninja is supported to build Chrome on Mac. If you just want to be able to run Chrome through Xcode, I would recommend instead using the xcode-ninja generator that is supported. This will create a Xcode project that will delegate the build to ninja.
I'm using the following:
$ export GYP_GENERATORS="ninja,xcode-ninja"
$ export GYP_GENERATOR_FLAGS="xcode_project_version=3.2 xcode_ninja_main_gyp=src/build/ninja/all.ninja.gyp"
$ gclient runhooks
$ open src/build/ninja/all.ninja.xcworkspace
Regards,
-- Sylvain