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

android_webview/native/aw_settings.cc

 // Copyright (c) 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 "android_webview/native/aw_settings.h"
 
 #include "android_webview/browser/aw_content_browser_client.h"
 #include "android_webview/browser/renderer_host/aw_render_view_host_ext.h"
 #include "android_webview/common/aw_content_client.h"
 #include "android_webview/native/aw_contents.h"
@@ skipping 420 matching lines @@
   web_prefs->record_whole_document =
       Java_AwSettings_getRecordFullDocument(env, obj);
 
   // TODO(jww): This should be removed once sufficient warning has been given of
   // possible API breakage because of disabling insecure use of geolocation.
   web_prefs->allow_geolocation_on_insecure_origins =
       Java_AwSettings_getAllowGeolocationOnInsecureOrigins(env, obj);
 
   // We use system scrollbars, so make Blink's scrollbars invisible.
   web_prefs->hide_scrollbars = true;
+
+  // Keep spellcheck disabled on html elements unless the spellcheck="true"
+  // attribute is explicitly specified. This "opt-in" behavior is for backward
+  // consistency in apps that use WebView (see crbug.com/652314).
+  web_prefs->spellcheck_enabled_by_default = false;
 }
 
 static jlong Init(JNIEnv* env,
                   const JavaParamRef<jobject>& obj,
                   const JavaParamRef<jobject>& web_contents) {
   content::WebContents* contents = content::WebContents::FromJavaWebContents(
       web_contents);
   AwSettings* settings = new AwSettings(env, obj, contents);
   return reinterpret_cast<intptr_t>(settings);
 }
 
 static ScopedJavaLocalRef<jstring> GetDefaultUserAgent(
     JNIEnv* env,
     const JavaParamRef<jclass>& clazz) {
   return base::android::ConvertUTF8ToJavaString(env, GetUserAgent());
 }
 
 bool RegisterAwSettings(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace android_webview