Add skeleton of content shell for android.

This is heavily based on http://codereview.chromium.org/9834037/ which added
an APK-based test runner for android. This CL adds a content_shell_apk target
for android containing an empty activity.

BUG=118591
TEST=build/test/install ContentShell-debug.apk on device

Review URL: http://codereview.chromium.org/9860032

git-svn-id: http://src.chromium.org/svn/trunk/src/build@129831 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

all_android.gyp

@@ -12,6 +12,7 @@
       'target_name': 'All',
       'type': 'none',
       'dependencies': [
+        '../content/content.gyp:content_shell_apk',
         'util/build_util.gyp:*',
         'android_builder_tests',
       ],