Introduce a v8::Platform class that bundles embedder callbacks

include/v8-platform.h

 // Copyright 2013 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
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 //       notice, this list of conditions and the following disclaimer.
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 //       with the distribution.
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-#ifndef V8_V8_DEFAULTS_H_
-#define V8_V8_DEFAULTS_H_
+#ifndef V8_V8_PLATFROM_H_
+#define V8_V8_PLATFORM_H_
 
 #include "v8.h"
 
-/**
- * Default configuration support for the V8 JavaScript engine.
- */
 namespace v8 {
 
-V8_DEPRECATED("Use ResourceConstraints::ConfigureDefaults instead",
-    bool V8_EXPORT ConfigureResourceConstraintsForCurrentPlatform(
-        ResourceConstraints* constraints));
+/**
+ * A Task represents a unit of work.
+ */
+class Task {
+ public:
+  virtual ~Task() {}
 
+  virtual void Run() = 0;
+};
 
-V8_DEPRECATED("Use ResourceConstraints::ConfigureDefaults instead",
-    bool V8_EXPORT SetDefaultResourceConstraintsForCurrentPlatform());
+/**
+ * V8 Platform abstraction layer.
+ *
+ * The embedder has to provide an implementation of this interface before
+ * initializing the rest of V8.
+ */
+class Platform {
+ public:
+  /**
+   * Schedules a task to be invoked on a background thread. |task_is_slow|
+   * indicates that the task will run a long time. The Platform implementation
+   * takes ownership of |task|. There is no guarantee about order of execution
+   * of tasks wrt order of scheduling, nor is there a guarantee about the
+   * thread the task will be run on.
+   */
+  virtual void CallOnBackgroundThread(Task* task, bool task_is_slow) = 0;
+
+  /**
+   * Schedules a task to be invoked on a foreground thread wrt a specific
+   * |isolate|. Tasks posted for the same isolate should be execute in order of
+   * scheduling. The definition of "foreground" is opaque to V8.
+   */
+  virtual void CallOnForegroundThread(Isolate* isolate, Task* task) = 0;
+
+ protected:
+  virtual ~Platform() {}
+};
 
 }  // namespace v8
 
-#endif  // V8_V8_DEFAULTS_H_
+#endif  // V8_V8_PLATFORM_H_