Pass and return GrColor4h by const& when possible

Bug: skia:
Change-Id: I8486d0631e4723f1a457a607bc21abd2581133d8
Reviewed-on: https://skia-review.googlesource.com/c/166562
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/src/gpu/ops/GrRegionOp.cpp b/src/gpu/ops/GrRegionOp.cpp
index 6ec230f..2ce89de 100644
--- a/src/gpu/ops/GrRegionOp.cpp
+++ b/src/gpu/ops/GrRegionOp.cpp
@@ -70,7 +70,7 @@
                                                aaType, stencilSettings);
     }
 
-    RegionOp(const Helper::MakeArgs& helperArgs, GrColor4h color, const SkMatrix& viewMatrix,
+    RegionOp(const Helper::MakeArgs& helperArgs, const GrColor4h& color, const SkMatrix& viewMatrix,
              const SkRegion& region, GrAAType aaType, const GrUserStencilSettings* stencilSettings)
             : INHERITED(ClassID())
             , fHelper(helperArgs, aaType, stencilSettings)