Pass alpha rather than full colors to TextureOps made from image sets.

Bug: skia:8563

Change-Id: Iff1a5544df7f5dfeca3bfa14723ce39e653007eb
Reviewed-on: https://skia-review.googlesource.com/c/171903
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/SkGpuDevice.cpp b/src/gpu/SkGpuDevice.cpp
index 8e88dfd..e36b0ce 100644
--- a/src/gpu/SkGpuDevice.cpp
+++ b/src/gpu/SkGpuDevice.cpp
@@ -1466,7 +1466,6 @@
     sampler.setFilterMode(kNone_SkFilterQuality == filterQuality ? GrSamplerState::Filter::kNearest
                                                                  : GrSamplerState::Filter::kBilerp);
     SkAutoTArray<GrRenderTargetContext::TextureSetEntry> textures(count);
-    SkPMColor4f color = { alpha, alpha, alpha, alpha };
     // We accumulate compatible proxies until we find an an incompatible one or reach the end and
     // issue the accumulated 'n' draws starting at 'base'.
     int base = 0, n = 0;
@@ -1476,7 +1475,7 @@
                     set[base].fImage->colorSpace(), set[base].fImage->alphaType(),
                     fRenderTargetContext->colorSpaceInfo().colorSpace(), kPremul_SkAlphaType);
             fRenderTargetContext->drawTextureSet(this->clip(), textures.get() + base, n,
-                                                 sampler.filter(), color, this->ctm(),
+                                                 sampler.filter(), alpha, this->ctm(),
                                                  std::move(textureXform));
         }
     };