Don't attempt to forward declare StringPiece.

content/public/common/content_client.h

Index: content/public/common/content_client.h
diff --git a/content/public/common/content_client.h b/content/public/common/content_client.h
index f984b47f409945116fe2a0f19ab0b6c4452b4c9f..b2460ba7c31c9eddff998d14dc3b7568e3a99b3f 100644
--- a/content/public/common/content_client.h
+++ b/content/public/common/content_client.h
@@ -11,6 +11,7 @@
 
 #include "base/basictypes.h"
 #include "base/string16.h"
+#include "base/string_piece.h"
 #include "build/build_config.h"
 #include "content/common/content_export.h"
 
@@ -21,10 +22,6 @@ namespace IPC {
 class Message;
 }
 
-namespace base {
-class StringPiece;
-}
-
 namespace sandbox {
 class TargetPolicy;
 }