Add templates for building java and running the jni_generator.

build/java.gypi

+# 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 file is meant to be included into a target to provide a rule
+# to build Java in a consistent manner.
+#
+# To use this, create a gyp target with the following form:
+# {
+#   'target_name': 'my-package_java',
+#   'type': 'none',
+#   'variables': {
+#     'package_name': 'my-package',
+#     'java_in_dir': 'path/to/package/root',
+#   },
+#   'includes': ['path/to/this/gypi/file'],
+# }
+#
+# Note that this assumes that there's ant buildfile with package_name in
+# java_in_dir. So if if you have package_name="base" and
+# java_in_dir="base/android/java" you should have a directory structure like:
+#
+# base/android/java/base.xml
+# base/android/java/org/chromium/base/Foo.java
+# base/android/java/org/chromium/base/Bar.java
+#
+# Finally, the generated jar-file will be:
+#   <(PRODUCT_DIR)/chromium_base.jar
+#
+# TODO(yfriedman): The "finally" statement isn't entirely true yet, as we don't
+# auto-generate the ant file yet.
+
+{
+  'actions': [
+    {
+      'action_name': 'ant_<(package_name)',
+      'message': 'Building <(package_name) java sources.',
+      'inputs': [
+         '<(java_in_dir)/<(package_name).xml',
+         '<!@(find <(java_in_dir) -name "*.java")'
+      ],
+      'outputs': [
+         '<(PRODUCT_DIR)/chromium_<(package_name).jar',
+      ],
+      'action': [
+        'ant',
+        '-DPRODUCT_DIR=<(PRODUCT_DIR)',
+        '-buildfile',
+        '<(java_in_dir)/<(package_name).xml',
+      ]
+    },
+  ],
+}