Add check to external string resource.

Extensions are a source of external strings where we don't perform check yet.

R=ulan@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/10878025

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12379 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -2539,7 +2539,7 @@ class V8EXPORT Extension {  // NOLINT
   // Note that the strings passed into this constructor must live as long
   // as the Extension itself.
   Extension(const char* name,
-            const char* source = 0,
+            const char* source,
             int dep_count = 0,
             const char** deps = 0,
             int source_length = -1);

src/api.cc

@@ -537,11 +537,13 @@ Extension::Extension(const char* name,
     : name_(name),
       source_length_(source_length >= 0 ?
                      source_length :
-                     (source ? static_cast<int>(strlen(source)) : 0)),
+                     static_cast<int>(strlen(source))),
       source_(source, source_length_),
       dep_count_(dep_count),
       deps_(deps),
-      auto_enable_(false) { }
+      auto_enable_(false) {
+  CHECK(source);
+}
 
 
 v8::Handle<Primitive> Undefined() {