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/GMBench.cpp b/bench/GMBench.cpp
index bcc83eb..57f0d3c 100644
--- a/bench/GMBench.cpp
+++ b/bench/GMBench.cpp
@@ -21,7 +21,7 @@
     return kNonRendering_Backend != backend;
 }
 
-void GMBench::onDraw(const int loops, SkCanvas* canvas) {
+void GMBench::onDraw(int loops, SkCanvas* canvas) {
     // Do we care about timing the draw of the background (once)?
     // Does the GM ever rely on drawBackground to lazily compute something?
     fGM->drawBackground(canvas);