Add a SetCanonicalCookie method for CookieMonster.

headless/public/util/testing/generic_url_request_mocks.cc

Index: headless/public/util/testing/generic_url_request_mocks.cc
diff --git a/headless/public/util/testing/generic_url_request_mocks.cc b/headless/public/util/testing/generic_url_request_mocks.cc
index 54f1ed9e44748f95f3f068fb0cc1f2575dcb78f7..8bddf5c65fe978f17f180dd38f9ccee0a25f4528 100644
--- a/headless/public/util/testing/generic_url_request_mocks.cc
+++ b/headless/public/util/testing/generic_url_request_mocks.cc
@@ -84,6 +84,14 @@ void MockCookieStore::SetCookieWithDetailsAsync(
   CHECK(false);
 }
 
+void MockCookieStore::SetCanonicalCookieAsync(
+    const net::CanonicalCookie& cookie,
+    bool secure_source,
+    bool can_modify_httponly,
+    const SetCookiesCallback& callback) {
+  CHECK(false);
+}
+
 void MockCookieStore::GetCookiesWithOptionsAsync(
     const GURL& url,
     const net::CookieOptions& options,