Implement touch control

tools/viewer/sk_app/android/Window_android.cpp

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #include "Window_android.h"
 
 #include "VulkanWindowContext_android.h"
@@ skipping 46 matching lines @@
     SkASSERT(window);
     ContextPlatformData_android platformData;
     platformData.fNativeWindow = window;
     fWindowContext = VulkanWindowContext::Create((void*)&platformData, fDisplayParams);
 }
 
 void Window_android::onDisplayDestroyed() {
     detach();
 }
 
-void Window_android::inval() { fSkiaAndroidApp->postMessage(Message(kContentInvalidated)); }
+void Window_android::inval() {
+    if (!fSkiaAndroidApp->fIsContentInvalidated) {
+        fSkiaAndroidApp->postMessage(Message(kContentInvalidated));
+        fSkiaAndroidApp->fIsContentInvalidated = true;
+    }
+}
 
 }   // namespace sk_app