Make GrRenderTask::numTargets non-virtual
Make GrRenderTask::numTargets non-virtual

Don't know why this was virtual, but it slowed down our clustering
substantially. Like, 25% slowdown on my desktop.

Bug: skia:10877
Change-Id: I67056d9c566c34562eb215d9abb7760a01baa3cb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/409417
Commit-Queue: Adlai Holler <74c8d5b16bacf4a5997d6535bb4043bbdfe052ea@google.com>
Auto-Submit: Adlai Holler <74c8d5b16bacf4a5997d6535bb4043bbdfe052ea@google.com>
Reviewed-by: Robert Phillips <95e8ac5504948c7bf91b22c16a8dbb7ae7c66bfd@google.com>

aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,google/skia