Quick fix: nullify Isolate in background parsing slightly later.

src/background-parsing-task.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_BACKGROUND_PARSING_TASK_H_
 #define V8_BACKGROUND_PARSING_TASK_H_
 
 #include <memory>
 
 #include "src/base/platform/platform.h"
 #include "src/base/platform/semaphore.h"
 #include "src/compiler.h"
 #include "src/parsing/parser.h"
 
 namespace v8 {
 namespace internal {
 
+class ScriptData;
+
 // Internal representation of v8::ScriptCompiler::StreamedSource. Contains all
 // data which needs to be transmitted between threads for background parsing,
 // finalizing it on the main thread, and compiling on the main thread.
 struct StreamedSource {
   StreamedSource(ScriptCompiler::ExternalSourceStream* source_stream,
                  ScriptCompiler::StreamedSource::Encoding encoding)
       : source_stream(source_stream), encoding(encoding) {}
 
   // Internal implementation of v8::ScriptCompiler::StreamedSource.
   std::unique_ptr<ScriptCompiler::ExternalSourceStream> source_stream;
@@ skipping 19 matching lines @@
  public:
   BackgroundParsingTask(StreamedSource* source,
                         ScriptCompiler::CompileOptions options, int stack_size,
                         Isolate* isolate);
 
   virtual void Run();
 
  private:
   StreamedSource* source_;  // Not owned.
   int stack_size_;
+  ScriptData* script_data_;
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_BACKGROUND_PARSING_TASK_H_