This adds an IDs map to the metadata cache, which maps package paths to
IDs. This is only ever used by the Import function in the type checker.
Change-Id: I8677d9439895bc6cbca5072e3fa9fddad4e165d5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/181683
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>