[DNR] Tentatively re-enable GetMatchedRules API test

This test was run at least 1000 times and no flakes have been observed.
Since the test code has changed as well, the test has been re-enabled to
see if it is still flaky on the trybots.

Bug: 1070344
Change-Id: I5350fe9292dbcb77ea8ddc6c230c1cec3b4e0378
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2219368
Auto-Submit: Kelvin Jiang <kelvinjiang@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773421}

chrome/browser/extensions/api/declarative_net_request/declarative_net_request_apitest.cc

@@ -56,8 +56,7 @@ IN_PROC_BROWSER_TEST_F(DeclarativeNetRequestAPItest, OnRulesMatchedDebug) {
   ASSERT_TRUE(RunExtensionTest("on_rules_matched_debug")) << message_;
 }
 
-// TODO(crbug.com/1070344): Disabled due to flakiness.
-IN_PROC_BROWSER_TEST_F(DeclarativeNetRequestAPItest, DISABLED_GetMatchedRules) {
+IN_PROC_BROWSER_TEST_F(DeclarativeNetRequestAPItest, GetMatchedRules) {
   ASSERT_TRUE(RunExtensionTest("get_matched_rules")) << message_;
 }