Assert there are some sources when running skpbench

Change-Id: I6009dfc7c6eabe04b3b6fdf68f38995d718b4fef
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/235278
Commit-Queue: Nathaniel Nifong <nifong@google.com>
Reviewed-by: Ben Wagner aka dogben <benjaminwagner@google.com>

tools/skpbench/_adb_path.py

@@ -27,7 +27,7 @@ def find_skps(skps):
   return __ADB.check('''\
     for PATHNAME in %s; do
       if [ -d "$PATHNAME" ]; then
-        find "$PATHNAME" -maxdepth 1 -name *.skp
+        find "$PATHNAME" -maxdepth 1 -name '*.skp' -o -name '*.mskp'
       else
         echo "$PATHNAME"
       fi

tools/skpbench/_os_path.py

@@ -17,6 +17,7 @@ def find_skps(skps):
   for skp in skps:
     if (path.isdir(skp)):
       pathnames.extend(glob.iglob(path.join(skp, '*.skp')))
+      pathnames.extend(glob.iglob(path.join(skp, '*.mskp')))
     else:
       pathnames.append(skp)
   return pathnames

tools/skpbench/skpbench.py

@@ -327,6 +327,7 @@ def main():
   DELIMITER = r'[, ](?!(?:[^(]*\([^)]*\))*[^()]*\))'
   configs = re.split(DELIMITER, FLAGS.config)
   srcs = _path.find_skps(FLAGS.srcs)
+  assert srcs
 
   if FLAGS.adb:
     adb = Adb(FLAGS.device_serial, FLAGS.adb_binary,