Move the event attach/detach logic on unload from event.js to

extensions/renderer/native_handler.cc

Index: extensions/renderer/native_handler.cc
diff --git a/extensions/renderer/native_handler.cc b/extensions/renderer/native_handler.cc
index 896ef568e1e2b9dfca64a63d9725d27d4d2e9b6f..a8b343ad58922a6752122651bf0afc03e23062ec 100644
--- a/extensions/renderer/native_handler.cc
+++ b/extensions/renderer/native_handler.cc
@@ -4,12 +4,19 @@
 
 #include "extensions/renderer/native_handler.h"
 
+#include "base/logging.h"
+
 namespace extensions {
 
 NativeHandler::NativeHandler() : is_valid_(true) {}
 
-NativeHandler::~NativeHandler() {}
+NativeHandler::~NativeHandler() {
+  CHECK(!is_valid_) << "NativeHandlers must be invalidated before destruction";
+}
 
-void NativeHandler::Invalidate() { is_valid_ = false; }
+void NativeHandler::Invalidate() {
+  CHECK(is_valid_);
+  is_valid_ = false;
+}
 
 }  // namespace extensions