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/ImageFilterCollapse.cpp b/bench/ImageFilterCollapse.cpp
index 010149b..2a2fa3a 100644
--- a/bench/ImageFilterCollapse.cpp
+++ b/bench/ImageFilterCollapse.cpp
@@ -39,7 +39,7 @@
         }
     }
 
-    void onDraw(const int loops, SkCanvas* canvas) override {
+    void onDraw(int loops, SkCanvas* canvas) override {
         makeBitmap();
 
         for(int i = 0; i < loops; i++) {