Remove //chrome dependency from ExtensionPrefs

extensions/browser/extensions_browser_client.h

Index: extensions/browser/extensions_browser_client.h
diff --git a/extensions/browser/extensions_browser_client.h b/extensions/browser/extensions_browser_client.h
index 2e3d26d8aede6914eb6d4679336179ee51ca8bcf..b9b2a2c6d4f3dec72a2c68e5e7ddd2f0c9b32045 100644
--- a/extensions/browser/extensions_browser_client.h
+++ b/extensions/browser/extensions_browser_client.h
@@ -28,6 +28,7 @@ class ApiActivityMonitor;
 class AppSorting;
 class Extension;
 class ExtensionHostDelegate;
+class ExtensionPrefs;
 class ExtensionSystem;
 class ExtensionSystemProvider;
 
@@ -129,6 +130,10 @@ class ExtensionsBrowserClient {
   virtual void RegisterExtensionFunctions(
       ExtensionFunctionRegistry* registry) const = 0;
 
+  // Registers client observers on each per-context ExtensionPrefs instance.
+  virtual void AddExtensionPrefsObservers(content::BrowserContext* context,
+                                          ExtensionPrefs* prefs) const = 0;
+
   // Returns the single instance of |this|.
   static ExtensionsBrowserClient* Get();