[interpreter] Switch context during stack unwinding.

src/frames.h

Index: src/frames.h
diff --git a/src/frames.h b/src/frames.h
index c1fdf3b1483013af22ef88dc36bfac76c73db8f2..92fe2723ea1791b085d6172a85daac2de4736b64 100644
--- a/src/frames.h
+++ b/src/frames.h
@@ -190,6 +190,7 @@ class InterpreterFrameConstants : public AllStatic {
 
   // Expression index for {StandardFrame::GetExpressionAddress}.
   static const int kBytecodeOffsetExpressionIndex = 1;
+  static const int kRegisterFileExpressionIndex = 2;
 
   // Register file pointer relative.
   static const int kLastParamFromRegisterPointer =
@@ -732,6 +733,9 @@ class InterpretedFrame : public JavaScriptFrame {
   // unwinding to continue execution at a different bytecode offset.
   void PatchBytecodeOffset(int new_offset);
 
+  // Access to the interpreter register file for this frame.
+  Object* GetInterpreterRegister(int register_index) const;
+
   // Build a list with summaries for this frame including all inlined frames.
   void Summarize(List<FrameSummary>* frames) override;