Add a nullable string16 class to base. It combines a string16 + a null param

in order to cover all the possible states of a WebKit string.  For strings
where the null state is not meaninfully different from the empty state, this
class should NOT be used.  There are, however, some cases where we do need to
track null.  LocalStorage is an example.  This class should be a fairly light
weight way to do so.  This change also adds implicit conversion to and from
WebStrings.

This also switches LocalStorage's IPCs over to using this new class.

BUG=17343
TEST=none

Review URL: http://codereview.chromium.org/174484

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@24574 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 27 insertions, 0 deletions

diff --git a/ipc/ipc_message_utils.h b/ipc/ipc_message_utils.h
index 5ec80a7..15d5297 100644
--- a/ipc/ipc_message_utils.h
+++ b/ipc/ipc_message_utils.h
@@ -11,6 +11,7 @@
 
 #include "base/file_path.h"
 #include "base/format_macros.h"
+#include "base/nullable_string16.h"
 #include "base/string16.h"
 #include "base/string_util.h"
 #include "base/time.h"
@@ -545,6 +546,32 @@ struct ParamTraits<std::pair<A, B> > {
   }
 };
 
+template <>
+struct ParamTraits<NullableString16> {
+  typedef NullableString16 param_type;
+  static void Write(Message* m, const param_type& p) {
+    WriteParam(m, p.string());
+    WriteParam(m, p.is_null());
+  }
+  static bool Read(const Message* m, void** iter, param_type* r) {
+    string16 string;
+    if (!ReadParam(m, iter, &string))
+      return false;
+    bool is_null;
+    if (!ReadParam(m, iter, &is_null))
+      return false;
+    *r = NullableString16(string, is_null);
+    return true;
+  }
+  static void Log(const param_type& p, std::wstring* l) {
+    l->append(L"(");
+    LogParam(p.string(), l);
+    l->append(L", ");
+    LogParam(p.is_null(), l);
+    l->append(L")");
+  }
+};
+
 // If WCHAR_T_IS_UTF16 is defined, then string16 is a std::wstring so we don't
 // need this trait.
 #if !defined(WCHAR_T_IS_UTF16)