Add BlimpContents[,Observer] and BlimpNavigationController

blimp/client/core/public/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("base") {
+source_set("public") {
   sources = [
-    "//ios/consumer/base/debugger.mm",
-    "//ios/public/consumer/base/debugger.h",
+    "blimp_contents.h",
+    "blimp_contents_observer.h",
+    "blimp_navigation_controller.h",
   ]
+
   deps = [
     "//base",
+    "//url",
   ]
 }