Skip unnecessary types when looking for id_refs.
Skip unnecessary types when looking for id_refs.

When searching for id_refs we are looking through types that will
never have id_refs. This adds a lot of extra work and overhead to
the search.

This patch takes the joinRefs operation on my Mac Air from ~3750ms to
~1450ms for the lthi_cats.json example.

BUG=211

Review URL: https://codereview.appspot.com/10036045

git-svn-id: 3a56fcae908c7e16d23cb53443ea4795ac387cf2@591 0e6d7f2b-9903-5b78-7403-59d27f066143

bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer