skpbench: add option for gpu timing

Adds a gpu timing option with a GL implementation.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2388433003

Committed: https://skia.googlesource.com/skia/+/c06720d06faab3b01eba1b8693e0ac791f06dc96
Review-Url: https://codereview.chromium.org/2388433003
diff --git a/tools/gpu/FenceSync.h b/tools/gpu/FenceSync.h
index 8f2bbe2..b430f5d 100644
--- a/tools/gpu/FenceSync.h
+++ b/tools/gpu/FenceSync.h
@@ -13,7 +13,7 @@
 namespace sk_gpu_test {
 
 using PlatformFence = uint64_t;
-static constexpr PlatformFence kInvalidPlatformFence = 0;
+static constexpr PlatformFence kInvalidFence = 0;
 
 /*
  * This class provides an interface to interact with fence syncs. A fence sync is an object that the
@@ -29,6 +29,6 @@
     virtual ~FenceSync() {}
 };
 
-}
+}  // namespace sk_gpu_test
 
 #endif