Don't attempt to forward declare StringPiece.

content/shell/shell.h

Index: content/shell/shell.h
diff --git a/content/shell/shell.h b/content/shell/shell.h
index 99d574884cbfa1111d7c55f84f226e5220f8f7c3..af5128c03f442ac37d311004e91dda0ef74f5a5f 100644
--- a/content/shell/shell.h
+++ b/content/shell/shell.h
@@ -11,6 +11,7 @@
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/string_piece.h"
 #include "content/browser/tab_contents/tab_contents_delegate.h"
 #include "ui/gfx/native_widget_types.h"
 
@@ -18,10 +19,6 @@ class GURL;
 class SiteInstance;
 class TabContents;
 
-namespace base {
-class StringPiece;
-}
-
 namespace content {
 
 class BrowserContext;