[interpreter] Switch context during stack unwinding.

src/frames.cc

Index: src/frames.cc
diff --git a/src/frames.cc b/src/frames.cc
index 4e499455f7eabb15295ba0c5f4e7e0bc19f5c900..def333dfcde6c23cce7cfcfddf4625959061a708 100644
--- a/src/frames.cc
+++ b/src/frames.cc
@@ -1163,6 +1163,13 @@ void InterpretedFrame::PatchBytecodeOffset(int new_offset) {
   SetExpression(index, Smi::FromInt(raw_offset));
 }
 
+Object* InterpretedFrame::GetInterpreterRegister(int register_index) const {
+  const int index = InterpreterFrameConstants::kRegisterFileExpressionIndex;
+  DCHECK_EQ(InterpreterFrameConstants::kRegisterFilePointerFromFp,
+            StandardFrameConstants::kExpressionsOffset - index * kPointerSize);
+  return GetExpression(index + register_index);
+}
+
 void InterpretedFrame::Summarize(List<FrameSummary>* functions) {
   DCHECK(functions->length() == 0);
   AbstractCode* abstract_code =