Track *all* external strings in the external string table.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 943dbbae56567a93cb82c2d244be68b1990a5bc2..290fcba97aa188a1fe1affb11ca1a4d3e86f62a7 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -5733,8 +5733,8 @@ bool v8::String::MakeExternal(v8::String::ExternalStringResource* resource) {
     external = obj;
   }
 
-  ASSERT(external->IsExternalString());
-  if (result && !external->IsInternalizedString()) {
+  if (result) {
+    ASSERT(external->IsExternalString());
     isolate->heap()->external_string_table()->AddString(*external);
   }
   return result;
@@ -5791,8 +5791,8 @@ bool v8::String::MakeExternal(
     external = obj;
   }
 
-  ASSERT(external->IsExternalString());
-  if (result && !external->IsInternalizedString()) {
+  if (result) {
+    ASSERT(external->IsExternalString());
     isolate->heap()->external_string_table()->AddString(*external);
   }
   return result;