Add preferences support for embedding applications

Applications can use brightray::BrowserContext::prefs to get access to
preferences that are persisted between launches.
brightray::BrowserContext::RegisterPrefs must be used to register preferences
before they're accessed.

Updated libchromiumcontent to pull in preferences support.

* vendor/libchromiumcontent 3944c1c...b6a0d85 (2):
  > Actually compile the base/prefs code
  > Export symbols from base/prefs

brightray/browser/browser_context.cc

@@ -8,6 +8,10 @@
 
 #include "base/files/file_path.h"
 #include "base/path_service.h"
+#include "base/prefs/json_pref_store.h"
+#include "base/prefs/pref_registry_simple.h"
+#include "base/prefs/pref_service.h"
+#include "base/prefs/pref_service_builder.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/resource_context.h"
 #include "content/public/browser/storage_partition.h"
@@ -36,6 +40,15 @@ private:
 };
 
 BrowserContext::BrowserContext() : resource_context_(new ResourceContext) {
+  auto prefs_path = GetPath().Append("Preferences");
+  PrefServiceBuilder builder;
+  builder.WithUserFilePrefs(prefs_path,
+      JsonPrefStore::GetTaskRunnerForFile(prefs_path, content::BrowserThread::GetBlockingPool()));
+
+  auto registry = make_scoped_refptr(new PrefRegistrySimple);
+  RegisterPrefs(registry);
+
+  prefs_.reset(builder.Create(registry));
 }
 
 BrowserContext::~BrowserContext() {

brightray/browser/browser_context.h

@@ -8,6 +8,9 @@
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/content_browser_client.h"
 
+class PrefRegistrySimple;
+class PrefService;
+
 namespace brightray {
 
 class URLRequestContextGetter;
@@ -19,6 +22,12 @@ public:
 
   net::URLRequestContextGetter* CreateRequestContext(content::ProtocolHandlerMap*);
 
+  PrefService* prefs() { return prefs_.get(); }
+
+protected:
+  // Subclasses should override this to register custom preferences.
+  virtual void RegisterPrefs(PrefRegistrySimple*) {}
+
 private:
   class ResourceContext;
 
@@ -37,6 +46,7 @@ private:
 
   scoped_ptr<ResourceContext> resource_context_;
   scoped_refptr<URLRequestContextGetter> url_request_getter_;
+  scoped_ptr<PrefService> prefs_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserContext);
 };