Move stats code to new layer (with configurable list of timers)

Bug: skia:
Change-Id: I3ca5c8c7047309983018339ec7b71b9aea5ee786
Reviewed-on: https://skia-review.googlesource.com/86921
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 96c7623..3f1ce7f 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1846,6 +1846,7 @@
         "tools/viewer/ImageSlide.cpp",
         "tools/viewer/SKPSlide.cpp",
         "tools/viewer/SampleSlide.cpp",
+        "tools/viewer/StatsLayer.cpp",
         "tools/viewer/Viewer.cpp",
       ]
       libs = []