Split out libplatform into a separate libary

include/v8-platform.h

Index: include/v8-platform.h
diff --git a/include/v8-platform.h b/include/v8-platform.h
index 5667211c3211bd07ada74c4bda8c2322c4810b63..d8ef044404c87aeb1211c4c024ad9fef11716560 100644
--- a/include/v8-platform.h
+++ b/include/v8-platform.h
@@ -37,6 +37,8 @@ class Platform {
     kLongRunningTask
   };
 
+  virtual ~Platform() {}
+
   /**
    * Schedules a task to be invoked on a background thread. |expected_runtime|
    * indicates that the task will run a long time. The Platform implementation
@@ -53,9 +55,6 @@ class Platform {
    * scheduling. The definition of "foreground" is opaque to V8.
    */
   virtual void CallOnForegroundThread(Isolate* isolate, Task* task) = 0;
-
- protected:
-  virtual ~Platform() {}
 };
 
 }  // namespace v8