Bench : Unused parameters cleanup

I removed unused parameters in bench wherever it was trivial to do so.
Review URL: https://codereview.appspot.com/7411046

git-svn-id: http://skia.googlecode.com/svn/trunk@7988 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/bench/DecodeBench.cpp b/bench/DecodeBench.cpp
index 6593d10..c87e6f6 100644
--- a/bench/DecodeBench.cpp
+++ b/bench/DecodeBench.cpp
@@ -40,7 +40,7 @@
         return fName.c_str();
     }
 
-    virtual void onDraw(SkCanvas* canvas) {
+    virtual void onDraw(SkCanvas*) {
         if (fFilename) {
             for (int i = 0; i < N; i++) {
                 SkBitmap bm;