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/ImageFilterDAGBench.cpp b/bench/ImageFilterDAGBench.cpp
index 47d59bc..74e23ef 100644
--- a/bench/ImageFilterDAGBench.cpp
+++ b/bench/ImageFilterDAGBench.cpp
@@ -25,7 +25,7 @@
         return "image_filter_dag";
     }
 
-    void onDraw(const int loops, SkCanvas* canvas) override {
+    void onDraw(int loops, SkCanvas* canvas) override {
         for (int j = 0; j < loops; j++) {
             SkAutoTUnref<SkImageFilter> blur(SkBlurImageFilter::Create(20.0f, 20.0f));
             SkImageFilter* inputs[kNumInputs];