Use SkPMColor4f throughout clear APIs

Bug: skia:
Change-Id: I5386e27edbcf39233880d869841a6632ecb9416c
Reviewed-on: https://skia-review.googlesource.com/c/168261
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/src/gpu/mtl/GrMtlGpuCommandBuffer.h b/src/gpu/mtl/GrMtlGpuCommandBuffer.h
index 9e1ce45..1505789 100644
--- a/src/gpu/mtl/GrMtlGpuCommandBuffer.h
+++ b/src/gpu/mtl/GrMtlGpuCommandBuffer.h
@@ -84,7 +84,7 @@
                 int meshCount,
                 const SkRect& bounds) override;
 
-    void onClear(const GrFixedClip& clip, GrColor color) override;
+    void onClear(const GrFixedClip& clip, const SkPMColor4f& color) override;
 
     void onClearStencilClip(const GrFixedClip& clip, bool insideStencilMask) override;