Introduce per-isolate assert scopes and API to guard JS execution.

src/execution.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 59 matching lines @@
 static Handle<Object> Invoke(bool is_construct,
                              Handle<JSFunction> function,
                              Handle<Object> receiver,
                              int argc,
                              Handle<Object> args[],
                              bool* has_pending_exception) {
   Isolate* isolate = function->GetIsolate();
 
   // Entering JavaScript.
   VMState<JS> state(isolate);
+  CHECK(AllowJavascriptExecution::IsAllowed(isolate));
 
   // Placeholder for return value.
   MaybeObject* value = reinterpret_cast<Object*>(kZapValue);
 
   typedef Object* (*JSEntryFunction)(byte* entry,
                                      Object* function,
                                      Object* receiver,
                                      int argc,
                                      Object*** args);
 
@@ skipping 959 matching lines @@
     ASSERT(isolate->concurrent_recompilation_enabled());
     stack_guard->Continue(INSTALL_CODE);
     isolate->optimizing_compiler_thread()->InstallOptimizedFunctions();
   }
   isolate->runtime_profiler()->OptimizeNow();
   return isolate->heap()->undefined_value();
 }
 
 
 } }  // namespace v8::internal