Dispose external string resource on heap teardown.

test/cctest/test-api.cc

Index: test/cctest/test-api.cc
diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index 761b402fa7dfe4d0d6bc3d022c6d54a1f71fd0fc..7803c873a18711126c07310b294ee50aa51415ef 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -17188,6 +17188,26 @@ TEST(VisitExternalStrings) {
 }
 
 
+TEST(ExternalStringCollectedAtTearDown) {
+  int destroyed = 0;
+  v8::Isolate* isolate = v8::Isolate::New();
+  { v8::Isolate::Scope isolate_scope(isolate);
+    v8::HandleScope handle_scope(isolate);
+    const char* s = "One string to test them all, one string to find them.";
+    TestAsciiResource* inscription =
+        new TestAsciiResource(i::StrDup(s), &destroyed);
+    v8::Local<v8::String> ring = v8::String::NewExternal(inscription);
+    // Ring is still alive.  Orcs are roaming freely across our lands.
+    CHECK_EQ(0, destroyed);
+    USE(ring);
+  }
+
+  isolate->Dispose();
+  // Ring has been destroyed.  Free Peoples of Middle-earth Rejoice.
+  CHECK_EQ(1, destroyed);
+}
+
+
 static double DoubleFromBits(uint64_t value) {
   double target;
   i::OS::MemCopy(&target, &value, sizeof(target));