[NetworkIdentifier] Use a more unique delimiter.

When separating ssid from security type in a serialized network
identifier, we were previously using an underscore.  Since this is an
allowed character in SSIDs, it's safer to use something more unique.

Bug: 966270
Change-Id: I3aac88bd3fc0cfa6058b021892a697e09b271cfb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1992585Reviewed-by: Azeem Arshad <azeemarshad@chromium.org>
Commit-Queue: Jon Mann <jonmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729921}

chromeos/components/sync_wifi/network_identifier.cc

@@ -18,7 +18,7 @@ namespace sync_wifi {
 
 namespace {
 
-const char kDelimeter[] = "_";
+const char kDelimeter[] = "<||>";
 
 }  // namespace
 

chromeos/components/sync_wifi/network_identifier_unittest.cc

@@ -39,7 +39,7 @@ TEST_F(NetworkIdentifierTest, FromProto) {
 }
 
 TEST_F(NetworkIdentifierTest, FromString) {
-  std::string string_id("0123456789ABCDEF_psk");
+  std::string string_id("0123456789ABCDEF<||>psk");
   NetworkIdentifier id = NetworkIdentifier::DeserializeFromString(string_id);
   EXPECT_EQ(kHexSsid, id.hex_ssid());
   EXPECT_EQ(shill::kSecurityPsk, id.security_type());