Add api call to determine whether a string can be externalized.

Review URL: http://codereview.chromium.org/164393

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2664 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -901,6 +901,11 @@ class V8EXPORT String : public Primitive {
    */
   bool MakeExternal(ExternalAsciiStringResource* resource);
 
+  /**
+   * Returns true if this string can be made external.
+   */
+  bool CanMakeExternal();
+
   /** Creates an undetectable string from the supplied ascii or utf-8 data.*/
   static Local<String> NewUndetectable(const char* data, int length = -1);
 

src/api.cc

@@ -2986,7 +2986,7 @@ bool v8::String::MakeExternal(v8::String::ExternalStringResource* resource) {
   if (IsDeadCheck("v8::String::MakeExternal()")) return false;
   if (this->IsExternal()) return false;  // Already an external string.
   ENTER_V8;
-  i::Handle <i::String> obj = Utils::OpenHandle(this);
+  i::Handle<i::String> obj = Utils::OpenHandle(this);
   bool result = obj->MakeExternal(resource);
   if (result && !obj->IsSymbol()) {
     // Operation was successful and the string is not a symbol. In this case
@@ -3022,7 +3022,7 @@ bool v8::String::MakeExternal(
   if (IsDeadCheck("v8::String::MakeExternal()")) return false;
   if (this->IsExternal()) return false;  // Already an external string.
   ENTER_V8;
-  i::Handle <i::String> obj = Utils::OpenHandle(this);
+  i::Handle<i::String> obj = Utils::OpenHandle(this);
   bool result = obj->MakeExternal(resource);
   if (result && !obj->IsSymbol()) {
     // Operation was successful and the string is not a symbol. In this case
@@ -3037,6 +3037,14 @@ bool v8::String::MakeExternal(
 }
 
 
+bool v8::String::CanMakeExternal() {
+  if (IsDeadCheck("v8::String::CanMakeExternal()")) return false;
+  i::Handle<i::String> obj = Utils::OpenHandle(this);
+  int size = obj->Size();  // Byte size of the original string.
+  return (size >= i::ExternalString::kSize) && !obj->IsExternalString();
+}
+
+
 Local<v8::Object> v8::Object::New() {
   EnsureInitialized("v8::Object::New()");
   LOG_API("Object::New");