Block internal PlatformEvents before they are dispatched in touchview.

ui/events/platform/platform_event_source.cc

Index: ui/events/platform/platform_event_source.cc
diff --git a/ui/events/platform/platform_event_source.cc b/ui/events/platform/platform_event_source.cc
index 9607ab78232e971d8b4b099829f5395b47722694..2f3efb981203b5f0e8c2b55e9eefd4cd3aebd0c6 100644
--- a/ui/events/platform/platform_event_source.cc
+++ b/ui/events/platform/platform_event_source.cc
@@ -8,6 +8,7 @@
 
 #include "base/message_loop/message_loop.h"
 #include "ui/events/platform/platform_event_dispatcher.h"
+#include "ui/events/platform/platform_event_filter.h"
 #include "ui/events/platform/platform_event_observer.h"
 #include "ui/events/platform/scoped_event_dispatcher.h"
 
@@ -62,9 +63,30 @@ void PlatformEventSource::RemovePlatformEventObserver(
   observers_.RemoveObserver(observer);
 }
 
+void PlatformEventSource::AddPlatformEventFilter(PlatformEventFilter* filter) {
+  CHECK(filter);
+  filters_.AddObserver(filter);
+}
+
+void PlatformEventSource::RemovePlatformEventFilter(
+    PlatformEventFilter* filter) {
+  filters_.RemoveObserver(filter);
+}
+
 uint32_t PlatformEventSource::DispatchEvent(PlatformEvent platform_event) {
   uint32_t action = POST_DISPATCH_PERFORM_DEFAULT;
 
+  // Always deliver all events to all PlatformEventFilters, if any of them
+  // specify that the event should not be dispatched, return immediately to
+  // stop propagation.
+  ObserverList<PlatformEventFilter>::Iterator iter(filters_);
+  while (PlatformEventFilter* filter = iter.GetNext()) {
+    if (!filter->ShouldDispatchEvent(platform_event))
+      action = POST_DISPATCH_STOP_PROPAGATION;
+  }
+  if (action == POST_DISPATCH_STOP_PROPAGATION)
+    return action;
+
   FOR_EACH_OBSERVER(PlatformEventObserver, observers_,
                     WillProcessEvent(platform_event));
   // Give the overridden dispatcher a chance to dispatch the event first.