Support more than just png files for diff images.

appengine/chromium_rietveld/new_static/diff/diff_parser_tests.js

Index: appengine/chromium_rietveld/new_static/diff/diff_parser_tests.js
diff --git a/appengine/chromium_rietveld/new_static/diff/diff_parser_tests.js b/appengine/chromium_rietveld/new_static/diff/diff_parser_tests.js
index cf12a03b72dc8ae689119ed97891109c1aec7aad..8e777b6eba45dfc3dc9bc4abf3dcd2a4a522ab7e 100644
--- a/appengine/chromium_rietveld/new_static/diff/diff_parser_tests.js
+++ b/appengine/chromium_rietveld/new_static/diff/diff_parser_tests.js
@@ -5,6 +5,16 @@
 "use strict";
 
 describe("DiffParser", function() {
+    it("should detect image file names", function() {
+        expect(DiffParser.isImageFile("foo.png")).toBeTruthy();
+        expect(DiffParser.isImageFile("foo.bar.jpeg")).toBeTruthy();
+        expect(DiffParser.isImageFile("foo(baz).jpg")).toBeTruthy();
+        expect(DiffParser.isImageFile("_foo_.webp")).toBeTruthy();
+        expect(DiffParser.isImageFile("example-file-name.bmp")).toBeTruthy();
+        expect(DiffParser.isImageFile("is a. gif.gif")).toBeTruthy();
+        expect(DiffParser.isImageFile(".gif")).toBeFalsy();
+        expect(DiffParser.isImageFile("not a gif.gif.txt")).toBeFalsy();
+    });
     it("should not show context link for file deletes", function() {
         var text =
             "Index: example.cc\n" +