Fix range-based for loops which copy the loop variable unnecessarily.

This will allow us to enable the ClangTidy check
performance-for-range-copy.

Change-Id: I11f152ffe458f5f353da8715ffd2fd47cf4e71a7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/306946
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
23 files changed