Fix cases of variable shadowing in /bench/.

If we manage to fix all the existing cases of variable shadowing, we
could enable -Wshadow.

Change-Id: I91187f35a33293914958fba1c0b3b6adf5364e19
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/438318
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Herb Derby <herb@google.com>
diff --git a/bench/ScalarBench.cpp b/bench/ScalarBench.cpp
index 9148532..e47fc63 100644
--- a/bench/ScalarBench.cpp
+++ b/bench/ScalarBench.cpp
@@ -150,7 +150,7 @@
 
     void onDraw(int loops, SkCanvas* canvas) override {
         SkRect r;
-        for (int i = 0; i < loops; ++i) {
+        for (int loop = 0; loop < loops; ++loop) {
             for (int i = 0; i < 1000; ++i) {
                 r.setBounds(fPts, PTS);
             }