[Android WebView] make spellcheck off by default and opt-in using spellcheck="true" attribute.

content/public/common/web_preferences.h

 // Copyright 2014 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.
 
 #ifndef CONTENT_PUBLIC_COMMON_WEB_PREFERENCES_H_
 #define CONTENT_PUBLIC_COMMON_WEB_PREFERENCES_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 220 matching lines @@
   bool viewport_meta_non_user_scalable_quirk;
   bool viewport_meta_zero_values_quirk;
   bool clobber_user_agent_initial_scale_quirk;
   bool ignore_main_frame_overflow_hidden_quirk;
   bool report_screen_size_in_physical_pixels_quirk;
   // Used by Android_WebView only to support legacy apps that inject script into
   // a top-level initial empty document and expect it to persist on navigation.
   bool resue_global_for_unowned_main_frame;
   bool autoplay_muted_videos_enabled;
   ProgressBarCompletion progress_bar_completion;
+  // Specifies default setting for spellcheck when the spellcheck attribute is
+  // not explicitly specified.
+  bool spellcheck_enabled_by_default;
 #endif
 
   // String that describes how media element autoplay behavior should be
   // affected by experiment.
   std::string autoplay_experiment_mode;
 
   // Default (used if the page or UA doesn't override these) values for page
   // scale limits. These are set directly on the WebView so there's no analogue
   // in WebSettings.
   float default_minimum_page_scale_factor;
   float default_maximum_page_scale_factor;
 
   // We try to keep the default values the same as the default values in
   // chrome, except for the cases where it would require lots of extra work for
   // the embedder to use the same default value.
   WebPreferences();
   WebPreferences(const WebPreferences& other);
   ~WebPreferences();
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_WEB_PREFERENCES_H_