Add a sys prop to control WebView Overlays support

The boolean system property is named as "debug.hwui.webview_overlays_enabled"

Bug: 192267127
Test: change the property value, check presence of Webview Surface
Control

Change-Id: I01e3e26282a5fa79aa504a6e49c5abe1a1c3ea02

libs/hwui/WebViewFunctorManager.cpp

@@ -121,7 +121,7 @@ void WebViewFunctor::drawGl(const DrawGlInfo& drawInfo) {
             .mergeTransaction = currentFunctor.mergeTransaction,
     };
 
-    if (!drawInfo.isLayer) {
+    if (Properties::enableWebViewOverlays && !drawInfo.isLayer) {
         renderthread::CanvasContext* activeContext =
                 renderthread::CanvasContext::getActiveContext();
         if (activeContext != nullptr) {