Move V8 snapshot loading code from isolate_holder to gin/v8_startup_data.{h,cc}.

gin/public/isolate_holder.h

Index: gin/public/isolate_holder.h
diff --git a/gin/public/isolate_holder.h b/gin/public/isolate_holder.h
index 7968b1df0ba3edd8a9978105b927a494ec4cb5ef..22e0b6bd8522cf2f5876adcaac5786ef920fa7ff 100644
--- a/gin/public/isolate_holder.h
+++ b/gin/public/isolate_holder.h
@@ -51,24 +51,6 @@ class GIN_EXPORT IsolateHolder {
   // thread.
   void RemoveRunMicrotasksObserver();
 
-#if defined(V8_USE_EXTERNAL_STARTUP_DATA)
-  static const int kV8SnapshotBasePathKey;
-  static const char kNativesFileName[];
-  static const char kSnapshotFileName[];
-
-  static bool LoadV8SnapshotFd(int natives_fd,
-                               int64 natives_offset,
-                               int64 natives_size,
-                               int snapshot_fd,
-                               int64 snapshot_offset,
-                               int64 snapshot_size);
-  static bool LoadV8Snapshot();
-#endif  // V8_USE_EXTERNAL_STARTUP_DATA
-  static void GetV8ExternalSnapshotData(const char** natives_data_out,
-                                        int* natives_size_out,
-                                        const char** snapshot_data_out,
-                                        int* snapshot_size_out);
-
  private:
   v8::Isolate* isolate_;
   scoped_ptr<PerIsolateData> isolate_data_;