Split SecurityExploitBrowserTest.InvalidRequestId into two

This is for further investigation of flakiness.

Bug: 799516
Change-Id: Ie31837422a4e0b8ed5926f8e669911b50721e2c9
Reviewed-on: https://chromium-review.googlesource.com/1123659Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572075}

content/browser/security_exploit_browsertest.cc

@@ -510,6 +510,9 @@ IN_PROC_BROWSER_TEST_F(SecurityExploitBrowserTest, InvalidOriginHeaders) {
 IN_PROC_BROWSER_TEST_F(SecurityExploitBrowserTest, InvalidRequestId) {
   // Existing loader in pending_loaders_.
   TryCreateDuplicateRequestIds(shell(), false);
+}
+
+IN_PROC_BROWSER_TEST_F(SecurityExploitBrowserTest, InvalidBlockedRequestId) {
   // Existing loader in blocked_loaders_map_.
   TryCreateDuplicateRequestIds(shell(), true);
 }