Move inval dedup to Window for wider usages.

tools/viewer/sk_app/Window.cpp

Index: tools/viewer/sk_app/Window.cpp
diff --git a/tools/viewer/sk_app/Window.cpp b/tools/viewer/sk_app/Window.cpp
index 0a7bcf8a70b75c0f5d61a4dfdb2b36408275e13d..f653420e5e4a2845185da2a610c17bddd1ca74db 100644
--- a/tools/viewer/sk_app/Window.cpp
+++ b/tools/viewer/sk_app/Window.cpp
@@ -63,6 +63,7 @@ bool Window::onTouch(int owner, InputState state, float x, float y) {
 }
 
 void Window::onPaint() {
+    fIsContentInvalidated = false;
     sk_sp<SkSurface> backbuffer = fWindowContext->getBackbufferSurface();
     if (backbuffer) {
         // draw into the canvas of this surface
@@ -92,4 +93,15 @@ void Window::setDisplayParams(const DisplayParams& params) {
     fWindowContext->setDisplayParams(params);
 }
 
+void Window::checkAndInval() {
+    if (!fIsContentInvalidated) {
+        fIsContentInvalidated = true;
+        inval();
+    }
+}
+
+void Window::uncheckInval() {
+    fIsContentInvalidated = false;
+}
+
 }   // namespace sk_app