Adds NetInfo v3 Web API to Blink.

Source/core/page/NetworkStateNotifier.h

Index: Source/core/page/NetworkStateNotifier.h
diff --git a/Source/core/page/NetworkStateNotifier.h b/Source/core/page/NetworkStateNotifier.h
index e60b93b64ff7636ee1e9cef386ce53ca59750f31..138aaf52dd24d29c9ce69ad0fa9bd7be9317b10b 100644
--- a/Source/core/page/NetworkStateNotifier.h
+++ b/Source/core/page/NetworkStateNotifier.h
@@ -69,8 +69,10 @@ public:
 
     void setWebConnectionType(blink::WebConnectionType);
 
-    // Must be called on the context's thread. An added observer must be
-    // removed before its ExecutionContext is deleted.
+    // Must be called on the context's thread. An added observer must be removed
+    // before its ExecutionContext is deleted. It's possible for an observer to
+    // be called twice for the same event if it is first removed and then added
+    // during notification.
     void addObserver(NetworkStateObserver*, ExecutionContext*);
     void removeObserver(NetworkStateObserver*, ExecutionContext*);