Fix Autofill hang when interacting with large forms (i.e. forms containing many fields).

chrome/renderer/autofill/form_autofill_util.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 "chrome/renderer/autofill/form_autofill_util.h"
 
 #include <map>
 
 #include "base/logging.h"
 #include "base/memory/scoped_vector.h"
@@ skipping 517 matching lines @@
     // Select the part of the text that the user didn't type.
     input_element->setSelectionRange(input_element->value().length(),
                                      input_element->suggestedValue().length());
   }
 }
 
 }  // namespace
 
 namespace autofill {
 
+const size_t kMaxParseableFields = 100;
+
 // In HTML5, all text fields except password are text input fields to
 // autocomplete.
 bool IsTextInput(const WebInputElement* element) {
   if (!element)
     return false;
 
   return element->isTextField() && !element->isPasswordField();
 }
 
 bool IsSelectElement(const WebFormControlElement& element) {
@@ skipping 162 matching lines @@
     FormField* form_field = new FormField;
     WebFormControlElementToFormField(control_element, extract_mask, form_field);
     form_fields.push_back(form_field);
     // TODO(jhawkins): A label element is mapped to a form control element's id.
     // field->name() will contain the id only if the name does not exist.  Add
     // an id() method to WebFormControlElement and use that here.
     name_map[form_field->name] = form_field;
     fields_extracted[i] = true;
   }
 
-  // If we failed to extract any fields, give up.
-  if (form_fields.empty())
+  // If we failed to extract any fields, give up.  Also, to avoid overly
+  // expensive computation, we impose a maximum number of allowable fields.
+  if (form_fields.empty() || form_fields.size() > kMaxParseableFields)
     return false;
 
   // Loop through the label elements inside the form element.  For each label
   // element, get the corresponding form control element, use the form control
   // element's name as a key into the <name, FormField> map to find the
   // previously created FormField and set the FormField's label to the
   // label.firstChild().nodeValue() of the label element.
   WebNodeList labels = form_element.getElementsByTagName("label");
   for (unsigned i = 0; i < labels.length(); ++i) {
     WebLabelElement label = labels.item(i).to<WebLabelElement>();
@@ skipping 160 matching lines @@
       continue;
 
     if (input_element->isAutofilled())
       return true;
   }
 
   return false;
 }
 
 }  // namespace autofill