Make optimus GPU detection more robust on Linux.
Make optimus GPU detection more robust on Linux.

Sometimes PCI scan fails to identify both Intel/NVIDIA GPUs, but if we identify the Intel GPU, and the NVIDIA driver, then we can safely claim it's a Intel/NVIDIA dual-GPU situatio.

BUG=140022
TEST=
Review URL: https://chromiumcodereview.appspot.com/10876022

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@152863 0039d316-1c4b-4281-b951-d872f2087c98

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