WebUI: Add JavaScript lifecycle-control to WebUIMessageHandler.

content/browser/webui/web_ui_message_handler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/public/browser/web_ui_message_handler.h"
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 
 namespace content {
 
+void WebUIMessageHandler::AllowJavascript() {
+  if (javascript_allowed_)
+    return;
+

[Dan Beam, 2016/04/18 23:13:20]

we should be checking this was called validly here as well, i.e.

CHECK(web_ui());
CHECK(web_ui()->SomeNewMethodThatChecksIfWeCanExecuteJavascript());

[tommycli, 2016/04/19 17:45:38]

Done.

+  javascript_allowed_ = true;
+  OnJavascriptAllowed();
+}
+
 bool WebUIMessageHandler::ExtractIntegerValue(const base::ListValue* value,
                                               int* out_int) {
   std::string string_value;
   if (value->GetString(0, &string_value))
     return base::StringToInt(string_value, out_int);
   double double_value;
   if (value->GetDouble(0, &double_value)) {
     *out_int = static_cast<int>(double_value);
     return true;
   }
@@ skipping 14 matching lines @@
 
 base::string16 WebUIMessageHandler::ExtractStringValue(
     const base::ListValue* value) {
   base::string16 string16_value;
   if (value->GetString(0, &string16_value))
     return string16_value;
   NOTREACHED();
   return base::string16();
 }
 
+void WebUIMessageHandler::RenderViewReused() {
+  if (!javascript_allowed_)
+    return;
+
+  javascript_allowed_ = false;
+  OnJavascriptDisallowed();
+}
+
 }  // namespace content