Re-enable HttpSecurityHeadersTest.UpdateDynamicPKPMaxAge0

This test was disabled on Windows due to flakiness. I ran it locally & on the try jobs, and neither gave any flakes, therefore, this CL re-enables the test.

BUG=375538

Review URL: https://codereview.chromium.org/948733002

Cr-Commit-Position: refs/heads/master@{#318177}

net/http/http_security_headers_unittest.cc

@@ -593,13 +593,7 @@ TEST_F(HttpSecurityHeadersTest, UpdateDynamicPKPOnly) {
   EXPECT_NE(new_dynamic_domain_state.pkp.spki_hashes.end(), hash);
 }
 
-// Failing on win_chromium_rel. crbug.com/375538
-#if defined(OS_WIN)
-#define MAYBE_UpdateDynamicPKPMaxAge0 DISABLED_UpdateDynamicPKPMaxAge0
-#else
-#define MAYBE_UpdateDynamicPKPMaxAge0 UpdateDynamicPKPMaxAge0
-#endif
-TEST_F(HttpSecurityHeadersTest, MAYBE_UpdateDynamicPKPMaxAge0) {
+TEST_F(HttpSecurityHeadersTest, UpdateDynamicPKPMaxAge0) {
   TransportSecurityState state;
   TransportSecurityState::DomainState static_domain_state;
 
@@ -677,7 +671,6 @@ TEST_F(HttpSecurityHeadersTest, MAYBE_UpdateDynamicPKPMaxAge0) {
                                &failure_log));
   EXPECT_NE(0UL, failure_log.length());
 }
-#undef MAYBE_UpdateDynamicPKPMaxAge0
 
 // Tests that when a static HSTS and a static HPKP entry are present, adding a
 // dynamic HSTS header does not clobber the static HPKP entry. Further, adding a