Add unittest for canonical host override.

Currently, when adding an alternative service with a new host, that host will
become the canonical host (if appropriate), override previous canonical hosts
for the same domain.  This CL adds a test to document this behavior.

BUG=392575

Review URL: https://codereview.chromium.org/1006813015

Cr-Commit-Position: refs/heads/master@{#322356}

net/http/http_server_properties_impl_unittest.cc

@@ -506,6 +506,22 @@ TEST_F(AlternateProtocolServerPropertiesTest, CanonicalBroken) {
   EXPECT_FALSE(HasAlternativeService(test_host_port_pair));
 }
 
+// Adding an alternative service for a new host overrides canonical host.
+TEST_F(AlternateProtocolServerPropertiesTest, CanonicalOverride) {
+  HostPortPair test_host_port_pair("foo.c.youtube.com", 80);
+  HostPortPair bar_host_port_pair("bar.c.youtube.com", 80);
+  AlternativeService bar_alternative_service(QUIC, "bar.c.youtube.com", 1234);
+  impl_.SetAlternativeService(bar_host_port_pair, bar_alternative_service, 1.0);
+  AlternativeService altsvc = impl_.GetAlternativeService(test_host_port_pair);
+  EXPECT_EQ(1234, altsvc.port);
+
+  HostPortPair qux_host_port_pair("qux.c.youtube.com", 80);
+  AlternativeService qux_alternative_service(QUIC, "qux.c.youtube.com", 443);
+  impl_.SetAlternativeService(qux_host_port_pair, qux_alternative_service, 1.0);
+  altsvc = impl_.GetAlternativeService(test_host_port_pair);
+  EXPECT_EQ(443, altsvc.port);
+}
+
 TEST_F(AlternateProtocolServerPropertiesTest, ClearWithCanonical) {
   HostPortPair test_host_port_pair("foo.c.youtube.com", 80);
   HostPortPair canonical_port_pair("bar.c.youtube.com", 80);