Add parentheses to appease -Wstring-concatenation

Bug: 1114873
Change-Id: I2a6c49bb74aedbd387dca743db0e7743cd284f82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2357757Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Arthur Eubanks <aeubanks@google.com>
Cr-Commit-Position: refs/heads/master@{#798351}

extensions/browser/api/web_request/form_data_parser_unittest.cc

@@ -187,8 +187,8 @@ TEST(WebRequestFormDataParserTest, Parsing) {
                           "select",
                           "one",
                           "binary",
-                          "\u0420\u043e\u0434\u0436\u0435\u0440 "
-                          "\u0416\u0435\u043b\u044f\u0437\u043d\u044b"};
+                          ("\u0420\u043e\u0434\u0436\u0435\u0440 "
+                           "\u0416\u0435\u043b\u044f\u0437\u043d\u044b")};
   const std::vector<std::string> kExpected(kPairs, kPairs + base::size(kPairs));
 
   std::vector<const base::StringPiece*> input;