Use swipe gesture to switch between slides on Android

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"
 
 namespace sk_app {
 
 Window* Window::CreateNativeWindow(void* platformData) {
     Window_android* window = new Window_android();
     if (!window->init((SkiaAndroidApp*)platformData)) {
         delete window;
         return nullptr;
     }
     return window;
 }
 
 bool Window_android::init(SkiaAndroidApp* skiaAndroidApp) {
     SkASSERT(skiaAndroidApp);
     fSkiaAndroidApp = skiaAndroidApp;
     fSkiaAndroidApp->fWindow = this;
     return true;
 }
 
+const DisplayParams& Window_android::getDisplayParams() {
+    if (fWindowContext) {
+        return fWindowContext->getDisplayParams();
+    } else {
+        // fWindowContext doesn't exist because we haven't
+        // initDisplay yet.
+        return fDisplayParams;
+    }
+}
+
 void Window_android::setTitle(const char* title) {
     //todo
     SkDebugf("Title: %s", title);
 }
 
 bool Window_android::attach(BackEndType attachType, const DisplayParams& params) {
     if (kVulkan_BackendType != attachType) {
         return false;
     }
 
     fDisplayParams = params;
 
     // We delay the creation of fTestContext until Android informs us that
     // the native window is ready to use.
     return true;
 }
 
 void Window_android::initDisplay(ANativeWindow* window) {
     SkASSERT(window);
     ContextPlatformData_android platformData;
     platformData.fNativeWindow = window;
     fWindowContext = VulkanWindowContext::Create((void*)&platformData, fDisplayParams);
-    fNativeWindowInitialized = true;
 }
 
 void Window_android::onDisplayDestroyed() {
-    fNativeWindowInitialized = false;
     detach();
 }
 
 void Window_android::inval() { fSkiaAndroidApp->postMessage(Message(kContentInvalidated)); }
 
 }   // namespace sk_app