Refactor IsolateHolder to be able to always create the isolate

gin/public/isolate_holder.h

 // Copyright 2013 The Chromium 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 GIN_PUBLIC_ISOLATE_HOLDER_H_
 #define GIN_PUBLIC_ISOLATE_HOLDER_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "gin/gin_export.h"
@@ skipping 14 matching lines @@
 //
 // It is not possible to mix the two.
 class GIN_EXPORT IsolateHolder {
  public:
   // Controls whether or not V8 should only accept strict mode scripts.
   enum ScriptMode {
     kNonStrictMode,
     kStrictMode
   };
 
-  explicit IsolateHolder(ScriptMode mode);
+  IsolateHolder();
+  // Deprecated.
   IsolateHolder(v8::Isolate* isolate, v8::ArrayBuffer::Allocator* allocator);
 
   ~IsolateHolder();
 
+  // Should be invoked once before creating IsolateHolder instances to
+  // initialize V8 and Gin.
+  static void Initialize(ScriptMode mode,
+                         v8::ArrayBuffer::Allocator* allocator);
+
   v8::Isolate* isolate() { return isolate_; }
 
  private:
   void Init(v8::ArrayBuffer::Allocator* allocator);
 
   bool isolate_owner_;
   v8::Isolate* isolate_;
   scoped_ptr<PerIsolateData> isolate_data_;
 
   DISALLOW_COPY_AND_ASSIGN(IsolateHolder);
 };
 
 }  // namespace gin
 
 #endif  // GIN_PUBLIC_ISOLATE_HOLDER_H_