Add a reset method to SkTMultiMap

This will be used as part of GrResourceAllocator::reset which
is coming in a followup CL.

Bug: skia:10877
Change-Id: I16327dd7e470e996891795a443fa665dd58cd54e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/397099
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>
1 file changed