[generators] Implement %GeneratorGetSourcePosition.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index a7aabe23e0f856b18734e09f3fe4f40c7b4b508d..0e00d0d1c4c352bf973de60efef21bf7a576ff9b 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -7363,23 +7363,29 @@ class JSGeneratorObject: public JSObject {
   // [receiver]: The receiver of the suspended computation.
   DECL_ACCESSORS(receiver, Object)
 
-  // [input]: The most recent input value.
+  // [input]: For active generators: the most recent input value.
+  // (For suspended new-style generators, we abuse this field to store debug
+  // information.)
   DECL_ACCESSORS(input, Object)
 
   // [resume_mode]: The most recent resume mode.
   enum ResumeMode { kNext, kReturn, kThrow };
   DECL_INT_ACCESSORS(resume_mode)
 
-  // [continuation]: Offset into code of continuation.
+  // [continuation]
   //
-  // A positive offset indicates a suspended generator.  The special
+  // A positive value indicates a suspended generator.  The special
   // kGeneratorExecuting and kGeneratorClosed values indicate that a generator
   // cannot be resumed.
   inline int continuation() const;
   inline void set_continuation(int continuation);
-  inline bool is_closed();
-  inline bool is_executing();
-  inline bool is_suspended();
+  inline bool is_closed() const;
+  inline bool is_executing() const;
+  inline bool is_suspended() const;
+
+  // For suspended generators: the source position at which the generator
+  // is suspended.
+  int source_position() const;
 
   // [operand_stack]: Saved operand stack.
   DECL_ACCESSORS(operand_stack, FixedArray)