Run GM benchs in bench mode

bench/GMBench.cpp

Index: bench/GMBench.cpp
diff --git a/bench/GMBench.cpp b/bench/GMBench.cpp
index 57b231653022823f9fa8d4794e2c9a3680021da2..6037a8221c2f62635ce1bc814ae6b1df53a4e630 100644
--- a/bench/GMBench.cpp
+++ b/bench/GMBench.cpp
@@ -22,6 +22,7 @@ bool GMBench::isSuitableFor(Backend backend) {
 }
 
 void GMBench::onDraw(int loops, SkCanvas* canvas) {
+    fGM->setMode(skiagm::GM::kBench_Mode);
     // 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);