CodeMod: google::ProgramUsage to gflags::ProgramUsage
CodeMod: google::ProgramUsage to gflags::ProgramUsage

Summary:
CodeMod: `google::ProgramUsage` to `gflags::ProgramUsage`.

For gflags, `namespace google` is deprecated in favor of `namespace gflags`.

Automated with:

```lang=bash
hg grep -lw google::ProgramUsage | xargs perl -pi -e 's,\bgoogle(::ProgramUsage)\b,gflags\1,g'
```

Reviewed By: igorsugak

Differential Revision: D4665851

fbshipit-source-id: 9790c74f1c42d74043b94ee356f8e3cc3622f132

bwasti/caffe2,caffe2/caffe2,pietern/caffe2,sf-wind/caffe2,davinwang/caffe2,pietern/caffe2,pietern/caffe2,Yangqing/caffe2,davinwang/caffe2,davinwang/caffe2,bwasti/caffe2,Yangqing/caffe2,sf-wind/caffe2,sf-wind/caffe2,davinwang/caffe2,xzturn/caffe2,xzturn/caffe2,bwasti/caffe2,xzturn/caffe2,pietern/caffe2,Yangqing/caffe2,bwasti/caffe2,pietern/caffe2,sf-wind/caffe2,sf-wind/caffe2,xzturn/caffe2,bwasti/caffe2,xzturn/caffe2,davinwang/caffe2,Yangqing/caffe2,Yangqing/caffe2