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
diff --git a/libs/hwui/Properties.h b/libs/hwui/Properties.h
index f5fd003..7df6e2c 100644
--- a/libs/hwui/Properties.h
+++ b/libs/hwui/Properties.h
@@ -182,6 +182,11 @@
  */
 #define PROPERTY_REDUCE_OPS_TASK_SPLITTING "renderthread.skia.reduceopstasksplitting"
 
+/**
+ * Enable WebView Overlays feature.
+ */
+#define PROPERTY_WEBVIEW_OVERLAYS_ENABLED "debug.hwui.webview_overlays_enabled"
+
 ///////////////////////////////////////////////////////////////////////////////
 // Misc
 ///////////////////////////////////////////////////////////////////////////////
@@ -276,6 +281,8 @@
     static bool useHintManager;
     static int targetCpuTimePercentage;
 
+    static bool enableWebViewOverlays;
+
     static StretchEffectBehavior getStretchEffectBehavior() {
         return stretchEffectBehavior;
     }