Make WebNode::to<Type>() (and toConst) casts contain type asserts.

components/autofill/content/renderer/form_autofill_util.cc

 // Copyright 2013 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 "components/autofill/content/renderer/form_autofill_util.h"
 
 #include <map>
 #include <set>
 
 #include "base/command_line.h"
@@ skipping 909 matching lines @@
 // label.firstChild().nodeValue() of the label element.
 void MatchLabelsAndFields(
     const WebElementCollection& labels,
     std::map<WebFormControlElement, FormFieldData*>* element_map) {
   CR_DEFINE_STATIC_LOCAL(WebString, kFor, ("for"));
   CR_DEFINE_STATIC_LOCAL(WebString, kHidden, ("hidden"));
 
   for (WebElement item = labels.firstItem(); !item.isNull();
        item = labels.nextItem()) {
     WebLabelElement label = item.to<WebLabelElement>();
-    WebFormControlElement field_element =
-        label.correspondingControl().to<WebFormControlElement>();
+    WebElement control = label.correspondingControl();
     FormFieldData* field_data = nullptr;
 
-    if (field_element.isNull()) {
+    if (control.isNull()) {
       // Sometimes site authors will incorrectly specify the corresponding
       // field element's name rather than its id, so we compensate here.
       base::string16 element_name = label.getAttribute(kFor);
       if (element_name.empty())
         continue;
       // Look through the list for elements with this name. There can actually
       // be more than one. In this case, the label may not be particularly
       // useful, so just discard it.
       for (const auto& iter : *element_map) {
         if (iter.second->name == element_name) {
           if (field_data) {
             field_data = nullptr;
             break;
           } else {
             field_data = iter.second;
           }
         }
       }
-    } else if (!field_element.isFormControlElement() ||
-               field_element.formControlType() == kHidden) {
-      continue;
-    } else {
+    } else if (control.isFormControlElement()) {
+      WebFormControlElement form_control = control.to<WebFormControlElement>();
+      if (form_control.formControlType() == kHidden)
+        continue;
       // Typical case: look up |field_data| in |element_map|.
-      auto iter = element_map->find(field_element);
+      auto iter = element_map->find(form_control);
       if (iter == element_map->end())
         continue;
       field_data = iter->second;
     }
 
     if (!field_data)
       continue;
 
     base::string16 label_text = FindChildText(label);
 
@@ skipping 562 matching lines @@
     size_t offset = GetTextSelectionStart(suggestion, user_input, false);
     // Zero selection start is for password manager, which can show usernames
     // that do not begin with the user input value.
     selection_start = (offset == base::string16::npos) ? 0 : offset;
   }
 
   input_element->setSelectionRange(selection_start, suggestion.length());
 }
 
 }  // namespace autofill