Move BenchTimer to tools as Timer

This breaks a bunch of circular dependencies between tools and gm and bench.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/4ed75287aed6371c6e4a41ffcc78c8a49c9810ed

CQ_EXTRA_TRYBOTS=tryserver.skia:Build-Mac10.7-Clang-Arm7-Debug-iOS-Trybot,Test-Ubuntu12-ShuttleA-GTX660-x86-Debug-Trybot
R=tfarina@chromium.org, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/344213003
diff --git a/tools/skpdiff/skpdiff_util.cpp b/tools/skpdiff/skpdiff_util.cpp
index 171721c..983bee2 100644
--- a/tools/skpdiff/skpdiff_util.cpp
+++ b/tools/skpdiff/skpdiff_util.cpp
@@ -83,7 +83,7 @@
 }
 #endif
 
-// TODO refactor BenchTimer to be used here
+// TODO refactor Timer to be used here
 double get_seconds() {
 #if SK_BUILD_FOR_WIN32
     LARGE_INTEGER currentTime;