Tighten up gradient clamp logic.
Tighten up gradient clamp logic.

This is just a little refactor.  Shouldn't change any logic or pixels.

Change-Id: I782df78f2d693dc7e35c286b049730e763aa3dc8
Reviewed-on: https://skia-review.googlesource.com/15653
Reviewed-by: Florin Malita <a8262bf13ea8c26821e91ea9bca6740a77c96dcd@chromium.org>
Reviewed-by: Herb Derby <9e12a3d2bbf73546e47cc9958f6ba8f3215b7eaf@google.com>
Commit-Queue: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@chromium.org>

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