Android: Add a webview-specific All target.

android_webview/all_webview.gyp

+# Copyright (c) 2012 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.
+
+# This is used as the top-level gyp file for building WebView in the Android
+# tree. It should depend only on native code, as we cannot currently generate
+# correct makefiles to build Java code via gyp in the Android tree.
+
+{
+  'targets': [
+    {
+      'target_name': 'All',
+      'type': 'none',
+      'dependencies': [
+        'android_webview.gyp:libwebview',
+      ],
+    }, # target_name: All
+  ],  # targets
+}