Introduce ViewRoot forwarding input/view events to native

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 1bb644606bd6368e7cd07ca18ceb87cd4a2c781d..d6f9690948a6996342a408205aed2d8153ba3bd9 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -995,6 +995,9 @@ const char kRendererWaitForJavaDebugger[] = "renderer-wait-for-java-debugger";
 
 // Enables overscrolling for the OSK on Android.
 const char kEnableOSKOverscroll[]               = "enable-osk-overscroll";
+
+// Enable new ViewRoot-based event forwarding.
+const char kEnableViewRoot[] = "enable-view-root";
 #endif
 
 // Enable the aggressive flushing of DOM Storage to minimize data loss.