Enable SafeBrowsingServiceMetadataTest.MalwareImg with MSAN

This test was disabled with MSAN due to the race condition in
OnReceivedThreatDOMDetails. Repeated local runs with MSAN now succeed,
so I think it's safe to re-enable.

Bug: 860445
Change-Id: I4d01568c79562ac1125c4410dbe2c52c17056c2d
Reviewed-on: https://chromium-review.googlesource.com/1149260Reviewed-by: Jialiu Lin <jialiul@chromium.org>
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577959}

chrome/browser/safe_browsing/safe_browsing_service_browsertest.cc

@@ -1043,14 +1043,7 @@ IN_PROC_BROWSER_TEST_P(SafeBrowsingServiceMetadataTest, MalwareIFrame) {
   EXPECT_TRUE(hit_report().is_subresource);
 }
 
-// TODO(https://crbug.com/860445) - Reenable this once potential race condition
-// is addressed, which is triggered in certain conditions under MSAN, see bug.
-#if defined(MEMORY_SANITIZER)
-#define MAYBE_MalwareImg DISABLED_MalwareImg
-#else
-#define MAYBE_MalwareImg MalwareImg
-#endif
-IN_PROC_BROWSER_TEST_P(SafeBrowsingServiceMetadataTest, MAYBE_MalwareImg) {
+IN_PROC_BROWSER_TEST_P(SafeBrowsingServiceMetadataTest, MalwareImg) {
   GURL main_url = embedded_test_server()->GetURL(kMalwarePage);
   GURL img_url = embedded_test_server()->GetURL(kMalwareImg);