gensupport directory here (excluding tests, add preserving the original
LICENSE) was copied verbatim from google-api-go-client.git, since the original
package is in internal now and no longer importable from luci-go.
This is a temporary solution until luci-go no longer depends on deprecated
Cloud Endpoints v1 APIs. Note that copied gensupport still depends on public
bits of google-api-go-client.git, so if they drift apart too much, stuff
will break.