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/WriterBench.cpp b/bench/WriterBench.cpp
index faf17b5..68c694e 100644
--- a/bench/WriterBench.cpp
+++ b/bench/WriterBench.cpp
@@ -21,7 +21,7 @@
         return "writer";
     }
 
-    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+    virtual void onDraw(SkCanvas*) SK_OVERRIDE {
         static const char gStr[] = "abcdefghimjklmnopqrstuvwxyz";
         static const size_t gLen = strlen(gStr);
         SkWriter32 writer(256 * 4);