Make HttpAuthHandler ctor public/@hide.

The Chromium WebView Provider needs to subclass HttpAuthHandler
so that we can adapt a ChromHttpAuthHandler into an
android.webkit.HttpAuthHandler. Currently the constructor (that
does nothing) is package private. So to satisfy the subclass
requirement, make it public, and to satisfy the API, make it
@hide.

Bug: 7034995
Change-Id: I9846aecacce078696db5be709394afb980eb25a6

core/java/android/webkit/HttpAuthHandler.java

@@ -28,9 +28,9 @@ import android.os.Handler;
 public class HttpAuthHandler extends Handler {
 
     /**
-     * Package-private constructor needed for API compatibility.
+     * @hide Only for use by WebViewProvider implementations.
      */
-    HttpAuthHandler() {
+    public HttpAuthHandler() {
     }
 
     /**