Declare this package strong-mode clean.

R=tjblasi@google.com

Review URL: https://codereview.chromium.org//1840423003 .

pkgs/string_scanner/.analysis_options

diff --git a/pkgs/string_scanner/.analysis_options b/pkgs/string_scanner/.analysis_options
new file mode 100644
index 0000000..a10d4c5
--- /dev/null
+++ b/pkgs/string_scanner/.analysis_options
@@ -0,0 +1,2 @@
+analyzer:
+  strong-mode: true