Remove const from `const int loops`.

This drives me nuts, and prevents `while (loops --> 0)`.

BUG=skia:

Review URL: https://codereview.chromium.org/1379923005
diff --git a/bench/Benchmark.h b/bench/Benchmark.h
index 06d42e8..00b05af 100644
--- a/bench/Benchmark.h
+++ b/bench/Benchmark.h
@@ -82,7 +82,7 @@
     void postDraw(SkCanvas*);
 
     // Bench framework can tune loops to be large enough for stable timing.
-    void draw(const int loops, SkCanvas*);
+    void draw(int loops, SkCanvas*);
 
     void setForceAlpha(int alpha) {
         fForceAlpha = alpha;
@@ -123,7 +123,7 @@
     virtual void onPostDraw(SkCanvas*) {}
     // Each bench should do its main work in a loop like this:
     //   for (int i = 0; i < loops; i++) { <work here> }
-    virtual void onDraw(const int loops, SkCanvas*) = 0;
+    virtual void onDraw(int loops, SkCanvas*) = 0;
 
     virtual SkIPoint onGetSize();