gh-pages "umbrella" package nav not active when Protobuf type is viewed

[quartzmo]

In the gh-pages docs (gcloud-common Angular site app), the left nav is not in the active (highlighted) state when a Protobuf type listed in the "Data Types" page is viewed.

Steps to reproduce:

1. Navigate to a "Data Types" left nav item in the google-cloud package, such as google-cloud/master/google/datastore/v1/datatypes.
2. In the table in the page shown, scroll downward and click the name of aGoogle::Protobuf type. The page for the type will display correctly, but the left nav will revert to its top-level view, with no item highlighted as active.