DNR tests: Return false in CreateVerifiedMatcher on seeing install warnings.

This helps debugging in tests when some rules fail to index correctly.

BUG=696822

Change-Id: I38be0f707e7de7b5a4be49aacb037b7d9bd42fbd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1911279
Commit-Queue: Kelvin Jiang <kelvinjiang@chromium.org>
Auto-Submit: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Kelvin Jiang <kelvinjiang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715110}

extensions/browser/api/declarative_net_request/test_utils.cc

@@ -129,6 +129,9 @@ bool CreateVerifiedMatcher(const std::vector<TestRule>& rules,
     return false;
   }
 
+  if (!result.warnings.empty())
+    return false;
+
   if (expected_checksum)
     *expected_checksum = result.ruleset_checksum;