Expose RenderFrameHost::GetLastCommittedOrigin().

It is an error to call this unless the RFH is current -- similar to
GetLastCommittedURL, but we actually enforce it.

There are two pending CLs that will want to use this: 1413853005 and 1465533008.

BUG=498580
[email protected]

Review URL: https://codereview.chromium.org/1475433002

Cr-Commit-Position: refs/heads/master@{#361722}
diff --git a/url/origin.h b/url/origin.h
index c94c38c..dc2f85f 100644
--- a/url/origin.h
+++ b/url/origin.h
@@ -117,7 +117,7 @@
   // matches; and neither is unique.
   bool IsSameOriginWith(const Origin& other) const;
 
-  // Allows SchemeHostPort to used as a key in STL (for example, a std::set or
+  // Allows Origin to be used as a key in STL (for example, a std::set or
   // std::map).
   bool operator<(const Origin& other) const;