Add 'autoplay' content settings and expose it to Blink.

chrome/renderer/content_settings_observer.h

Index: chrome/renderer/content_settings_observer.h
diff --git a/chrome/renderer/content_settings_observer.h b/chrome/renderer/content_settings_observer.h
index 97af499407e56bd326bb262e5670097827162e45..f5b88c88f9ba877c850971e8bd6d739f97dfbcd4 100644
--- a/chrome/renderer/content_settings_observer.h
+++ b/chrome/renderer/content_settings_observer.h
@@ -42,9 +42,9 @@ class ContentSettingsObserver
                           bool should_whitelist);
   ~ContentSettingsObserver() override;
 
-  // Sets the content setting rules which back |AllowImage()|, |AllowScript()|,
-  // and |AllowScriptFromSource()|. |content_setting_rules| must outlive this
-  // |ContentSettingsObserver|.
+  // Sets the content setting rules which back |allowImage()|, |allowScript()|,
+  // |allowScriptFromSource()| and |allowAutoplay()|. |content_setting_rules|
+  // must outlive this |ContentSettingsObserver|.
   void SetContentSettingRules(
       const RendererContentSettingRules* content_setting_rules);
 
@@ -84,6 +84,7 @@ class ContentSettingsObserver
   bool allowRunningInsecureContent(bool allowed_per_settings,
                                    const blink::WebSecurityOrigin& context,
                                    const blink::WebURL& url) override;
+  bool allowAutoplay(bool default_value) override;
 
  private:
   FRIEND_TEST_ALL_PREFIXES(ContentSettingsObserverTest, WhitelistedSchemes);