Add a basic UI to the Android Blimp client.

blimp/common/proto/navigation.proto

Index: blimp/common/proto/navigation.proto
diff --git a/blimp/common/proto/navigation.proto b/blimp/common/proto/navigation.proto
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+// Copyright 2015 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.
+//
+// Message definitions for browser navigation messages.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package blimp;
+
+message LoadUrlMessage {
+  // The text to generate and create a URL from.  This might be a URL or might
+  // not.  It might be text that should be turned into a search URL.
+  optional string url = 1;
+}
+
+message NavigationStateChangeMessage {
+  // If the URL changed, this will include the new URL string.
+  optional string url = 1;
+
+  // If the favicon of the page changed, this should include the serialized
+  // bitmap of the favicon.
+  optional bytes favicon = 2;
+
+  // If the title changed, this will contain the new title string.
+  optional string title = 3;
+}
+
+message NavigationMessage {
+  enum Type {
+    // Server => Client types.
+    NAVIGATION_STATE_CHANGED = 1;
+
+    // Client => Server types.
+    LOAD_URL = 2;
+    GO_BACK = 3;
+    RELOAD = 4;
+  }
+
+  optional Type type = 1;
+
+  optional NavigationStateChangeMessage navigation_state_change = 1000;
+  optional LoadUrlMessage load_url = 1001;
+}