Support resize in Android Viewer App

tools/viewer/sk_app/android/GLWindowContext_android.h

Index: tools/viewer/sk_app/android/GLWindowContext_android.h
diff --git a/tools/viewer/sk_app/android/GLWindowContext_android.h b/tools/viewer/sk_app/android/GLWindowContext_android.h
index 85e65beaa251b451cb41ab3d98d0cc33f178496c..5f4c031ed1b44f22c8782574a08a4aafe6541722 100644
--- a/tools/viewer/sk_app/android/GLWindowContext_android.h
+++ b/tools/viewer/sk_app/android/GLWindowContext_android.h
@@ -13,6 +13,8 @@
 
 #include <EGL/egl.h>
 
+struct ANativeWindow;
+
 namespace sk_app {
 
 class GLWindowContext_android : public GLWindowContext {
@@ -32,6 +34,9 @@ private:
     EGLDisplay fDisplay;
     EGLContext fEGLContext;
     EGLSurface fSurface;
+
+    // For setDisplayParams and resize which call onInitializeContext with null platformData
+    ANativeWindow* fNativeWindow = nullptr;
 };