Improve SkCanvas::temporary_internal_getRgnClip performance
Improve SkCanvas::temporary_internal_getRgnClip performance

Improve temporary_internal_getRgnClip performance for rect clips
by avoiding SkClipStack::asPath.

BUG=skia:

Change-Id: I371ac6031df325646841d57c4afaba7b835a12bb
Reviewed-on: https://skia-review.googlesource.com/8688
Commit-Queue: Stan Iliev <e0755a3e69d99fdad882cb8e8dbf4e139b1441bb@google.com>
Reviewed-by: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>
Reviewed-by: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>

Hikari-no-Tenshi/android_external_skia,google/skia,HalCanary/skia-hc,google/skia,google/skia,rubenvb/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,rubenvb/skia,HalCanary/skia-hc,rubenvb/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,rubenvb/skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,google/skia,rubenvb/skia,google/skia,HalCanary/skia-hc,HalCanary/skia-hc,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,google/skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,rubenvb/skia,rubenvb/skia,google/skia,google/skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia