tools: Make ETC baseline opt in in gltfbasis

These baselines are very helpful to analyze a small set of files but
very distracting on a large set of files, so make this opt in via a
command line argument.

tools/gltfbasis.py

@@ -11,6 +11,7 @@
 argp = argparse.ArgumentParser()
 argp.add_argument('--basisu', type=str, required=True)
 argp.add_argument('--graph', type=str, default="basisu.png")
+argp.add_argument('--etcbase', action='store_true')
 argp.add_argument('files', type=str, nargs='+')
 args = argp.parse_args()
 
@@ -55,11 +56,11 @@ def stats(path):
 for path in args.files:
     print('Processing', path)
     results = stats(path)
-    etcbase = compress(path, ["-q", "192"])
+    etcbase = compress(path, ["-q", "192"]) if args.etcbase else None
 
     for idx, field in enumerate(fields):
         line, = axs[idx].plot([r['rdo_l'] for r in results], [r[field] for r in results])
-        if field in etcbase:
+        if etcbase and field in etcbase:
             axs[idx].axhline(etcbase[field], color=line.get_color(), linestyle='dotted')
         if idx == 0:
             lines.append(line)