Mark all methods on SkXfermode as const, in preparation for declaring all
xfermodes as immutable/reentrant-safe
Review URL: https://codereview.appspot.com/6941065

git-svn-id: http://skia.googlecode.com/svn/trunk@6855 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkArithmeticMode.cpp b/src/effects/SkArithmeticMode.cpp
index c999ce0..54a28ce 100644
--- a/src/effects/SkArithmeticMode.cpp
+++ b/src/effects/SkArithmeticMode.cpp
@@ -12,7 +12,7 @@
     }
 
     virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
-                        const SkAlpha aa[]) SK_OVERRIDE;
+                        const SkAlpha aa[]) const SK_OVERRIDE;
 
     SK_DECLARE_UNFLATTENABLE_OBJECT()
 
@@ -48,7 +48,7 @@
 }
 
 void SkArithmeticMode_scalar::xfer32(SkPMColor dst[], const SkPMColor src[],
-                                     int count, const SkAlpha aaCoverage[]) {
+                                 int count, const SkAlpha aaCoverage[]) const {
     SkScalar k1 = fK[0] / 255;
     SkScalar k2 = fK[1];
     SkScalar k3 = fK[2];