PPAPI: Reduce string copying in SerializedVar.

ppapi/shared_impl/var.cc

Index: ppapi/shared_impl/var.cc
diff --git a/ppapi/shared_impl/var.cc b/ppapi/shared_impl/var.cc
index 60d439bd6b3f0099830a6a33b5e5c3c40030ac2d..3fce7e3180fadf8102f56ddf4388c3455cfa845c 100644
--- a/ppapi/shared_impl/var.cc
+++ b/ppapi/shared_impl/var.cc
@@ -124,6 +124,11 @@ StringVar::StringVar(const char* str, uint32 len)
 StringVar::~StringVar() {
 }
 
+StringVar::StringVar(scoped_ptr<std::string> str) {
+  // Swap the given string's contents in to value to avoid copying.
+  str->swap(value_);
+}
+
 StringVar* StringVar::AsStringVar() {
   return this;
 }
@@ -146,6 +151,17 @@ PP_Var StringVar::StringToPPVar(const char* data, uint32 len) {
 }
 
 // static
+PP_Var StringVar::StringToPPVar(scoped_ptr<std::string> str) {
+  DCHECK(str.get());
+  if (!str.get())
+    return PP_MakeNull();
+  scoped_refptr<StringVar> str_var(new StringVar(str.Pass()));
+  if (!str_var || !IsStringUTF8(str_var->value()))
+    return PP_MakeNull();
+  return str_var->GetPPVar();
+}
+
+// static
 StringVar* StringVar::FromPPVar(PP_Var var) {
   if (var.type != PP_VARTYPE_STRING)
     return NULL;