chrome: Support configuration of accept language (see issue #2969)

This change adds support for CEF settings configuration of accept_language_list.
If specified, this value will take precedence over the "intl.accept_languages"
preference which is controlled by chrome://settings/languages.

libcef/browser/prefs/browser_prefs.h

@@ -11,6 +11,8 @@ namespace base {
 class FilePath;
 }
 
+class CefBrowserContext;
+class CefBrowserHostBase;
 class PrefRegistrySimple;
 class PrefService;
 class Profile;
@@ -29,8 +31,12 @@ std::unique_ptr<PrefService> CreatePrefService(Profile* profile,
                                                const base::FilePath& cache_path,
                                                bool persist_user_preferences);
 
-// Set language preferences on |profile|.
-void SetLanguagePrefs(Profile* profile);
+// Returns the value for populating the accept-language HTTP request header.
+// |browser_context| and/or |browser| may be nullptr. If |expand| is true then
+// base languages and Q values may be added.
+std::string GetAcceptLanguageList(CefBrowserContext* browser_context,
+                                  CefBrowserHostBase* browser,
+                                  bool expand);
 
 }  // namespace browser_prefs