Reland of Pass --images '' to nanobench to disable image benchmarking.

tools/nanobench_flags.py

Index: tools/nanobench_flags.py
diff --git a/tools/nanobench_flags.py b/tools/nanobench_flags.py
index f11ea1f0f1f936965f273ab3c524de925c87399a..f5902426865bbea24081b0128bf0e088aa2e5095 100755
--- a/tools/nanobench_flags.py
+++ b/tools/nanobench_flags.py
@@ -28,6 +28,9 @@
 cov_start = lineno()+1   # We care about coverage starting just past this def.
 def get_args(bot):
   args = []
+
+  # Temporarily disable image benchmarking.
+  args.append('--images')
 
   if 'Appurify' not in bot:
     args.extend(['--scales', '1.0', '1.1'])