ONC: Add ExtraHosts property to OpenVPN

This is needed to support multiple fallback hosts.

BUG=742666
TEST=Modified translator and validator unit tests to include
checks for ExtraHosts

Change-Id: I3faa20fb5d3f3ca490340527ad0a40a7fe9f837a
Reviewed-on: https://chromium-review.googlesource.com/720138
Reviewed-by: Kevin Cernekee <[email protected]>
Reviewed-by: Steven Bennetts <[email protected]>
Commit-Queue: Matthew Wang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#509536}
diff --git a/components/onc/onc_constants.cc b/components/onc/onc_constants.cc
index 55261d7..b6456bb 100644
--- a/components/onc/onc_constants.cc
+++ b/components/onc/onc_constants.cc
@@ -361,6 +361,7 @@
 const char kCipher[] = "Cipher";
 const char kCompLZO[] = "CompLZO";
 const char kCompNoAdapt[] = "CompNoAdapt";
+const char kExtraHosts[] = "ExtraHosts";
 const char kIgnoreDefaultRoute[] = "IgnoreDefaultRoute";
 const char kInteract[] = "interact";
 const char kKeyDirection[] = "KeyDirection";