Don't touch the prototype chain to get the private script controller.

third_party/WebKit/Source/bindings/core/v8/PrivateScriptRunner.cpp

Index: third_party/WebKit/Source/bindings/core/v8/PrivateScriptRunner.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/PrivateScriptRunner.cpp b/third_party/WebKit/Source/bindings/core/v8/PrivateScriptRunner.cpp
index 77b88f46afa5d47ffc73ea9549231bf1216244de..8bf2fdab65060216bc0e0502bd6d7d2fc7635d43 100644
--- a/third_party/WebKit/Source/bindings/core/v8/PrivateScriptRunner.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/PrivateScriptRunner.cpp
@@ -57,12 +57,12 @@ static v8::Local<v8::Value> compileAndRunPrivateScript(ScriptState* scriptState,
 
   v8::Local<v8::Context> context = scriptState->context();
   v8::Local<v8::Object> global = context->Global();
-  v8::Local<v8::Value> privateScriptController =
-      global->Get(context, v8String(isolate, "privateScriptController"))
-          .ToLocalChecked();
-  RELEASE_ASSERT(privateScriptController->IsUndefined() ||
-                 privateScriptController->IsObject());
-  if (privateScriptController->IsObject()) {
+  v8::Local<v8::String> key = v8String(isolate, "privateScriptController");
+
+  if (v8CallBoolean(global->HasOwnProperty(context, key))) {

[Yuki, 2016/11/28 05:13:34]

nit: v8CallBoolean is obsolete.
Please use V8 APIs directly.

[Mariusz Mlynski, 2016/11/28 07:51:44]

Done. Btw, there's no deprecation note for v8CallBoolean in V8BindingMacros.h,
so one might be needed to prevent further usage.

[Yuki, 2016/11/28 08:01:29]

Acknowledged.

+    v8::Local<v8::Value> privateScriptController =
+        global->Get(context, key).ToLocalChecked();
+    CHECK(privateScriptController->IsObject());
     v8::Local<v8::Object> privateScriptControllerObject =
         privateScriptController.As<v8::Object>();
     v8::Local<v8::Value> importFunctionValue =