Block modal dialogs inside sandboxes.

Source/core/dom/SandboxFlags.cpp

 /*
  * Copyright (C) 2013 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 50 matching lines @@
         } else if (equalIgnoringCase(sandboxToken, "allow-top-navigation")) {
             flags &= ~SandboxTopNavigation;
         } else if (equalIgnoringCase(sandboxToken, "allow-popups")) {
             flags &= ~SandboxPopups;
         } else if (equalIgnoringCase(sandboxToken, "allow-pointer-lock")) {
             flags &= ~SandboxPointerLock;
         } else if (equalIgnoringCase(sandboxToken, "allow-orientation-lock")) {
             flags &= ~SandboxOrientationLock;
         } else if (equalIgnoringCase(sandboxToken, "allow-unsandboxed-auxiliary") && RuntimeEnabledFeatures::unsandboxedAuxiliaryEnabled()) {
             flags &= ~SandboxPropagatesToAuxiliaryBrowsingContexts;
+        } else if (equalIgnoringCase(sandboxToken, "allow-modals") && RuntimeEnabledFeatures::sandboxBlocksModalsEnabled()) {
+            flags &= ~SandboxModals;
         } else {
             if (numberOfTokenErrors)
                 tokenErrors.appendLiteral(", '");
             else
                 tokenErrors.append('\'');
             tokenErrors.append(sandboxToken);
             tokenErrors.append('\'');
             numberOfTokenErrors++;
         }
     }
 
     if (numberOfTokenErrors) {
         if (numberOfTokenErrors > 1)
             tokenErrors.appendLiteral(" are invalid sandbox flags.");
         else
             tokenErrors.appendLiteral(" is an invalid sandbox flag.");
         invalidTokensErrorMessage = tokenErrors.toString();
     }
 
     return flags;
 }
 
 }