Only perform matrix concat when actually logging histograms

Bug: skia:
Change-Id: I61a710b570601d0d1178cf1dbe0d46d20872e9f1
Reviewed-on: https://skia-review.googlesource.com/c/193364
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
5 files changed