In Manhattan the test generates a bunch of queries that it doesn't
start until later frames. In ANGLE these queries will be stored as
nullptr entries in the QueryMap. By default the QueryMap Iterator skips
over nullptr entries. This manifested later as GL errors during replay.

Fix this by adding a new Iterator type to ResourceMap that does not
skip over nullptr values.

Bug: angleproject:4489
Change-Id: If56b908fb233de0df0445f9ea19fc322f2c42976
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2107762
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>