chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/extension_service.h

Index: chrome/browser/extensions/extension_service.h
diff --git a/chrome/browser/extensions/extension_service.h b/chrome/browser/extensions/extension_service.h
index 3235cab979f789be834ef87fd5d66e4203d2cc8d..75d87fb54da352030a89e80f3c73f9101402f828 100644
--- a/chrome/browser/extensions/extension_service.h
+++ b/chrome/browser/extensions/extension_service.h
@@ -40,14 +40,12 @@
 #error "Extensions must be enabled"
 #endif
 
-class GURL;
 class HostContentSettingsMap;
 class Profile;
 
 namespace base {
 class CommandLine;
 class SequencedTaskRunner;
-class Version;
 }
 
 namespace content {
@@ -59,8 +57,6 @@ class AppDataMigrator;
 class ComponentLoader;
 class CrxInstaller;
 class ExtensionActionStorageManager;
-class ExtensionDownloader;
-class ExtensionDownloaderDelegate;
 class ExtensionErrorController;
 class ExtensionRegistry;
 class ExtensionSystem;