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/ChecksumBench.cpp b/bench/ChecksumBench.cpp
index c731a8f..a2c2824 100644
--- a/bench/ChecksumBench.cpp
+++ b/bench/ChecksumBench.cpp
@@ -51,7 +51,7 @@
         }
     }
 
-    void onDraw(const int loops, SkCanvas*) override {
+    void onDraw(int loops, SkCanvas*) override {
         switch (fType) {
             case kChecksum_ChecksumType: {
                 for (int i = 0; i < loops; i++) {