Add a snapshot of flutter/engine/src/build to our sdk

build/android/adb_run_android_webview_shell

Index: build/android/adb_run_android_webview_shell
diff --git a/build/android/adb_run_android_webview_shell b/build/android/adb_run_android_webview_shell
new file mode 100755
index 0000000000000000000000000000000000000000..1014a731f476608d8944c83bdc28ac8d6c2f0510
--- /dev/null
+++ b/build/android/adb_run_android_webview_shell
@@ -0,0 +1,12 @@
+#!/bin/bash
+#
+# Copyright (c) 2013 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.
+
+optional_url=$1
+
+adb shell am start \
+  -a android.intent.action.VIEW \
+  -n org.chromium.android_webview.shell/.AwShellActivity \
+  ${optional_url:+-d "$optional_url"}