Don't attempt to forward declare StringPiece.

1) This is discouraged because it prevents callers from benefiting from automatic coersion from string/char* types.
2) A follow-up CL (http://codereview.chromium.org/8659047/) will make StringPiece a template, and thus awkward to forward declare. The very small number of places that were appropriately forward declaring it do not justify writing a 'string_piece_forward.h'.

BUG=87634
R=jam@chromium.org


Review URL: http://codereview.chromium.org/8818014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113403 0039d316-1c4b-4281-b951-d872f2087c98

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;
 }