Support 'restart call frame' debug command

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 95bc313d22d3c5cf67e20aa8f853106a92d1bdf9..5b44374591cefb4a10a25e89b7c1e90d365d6817 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -12789,6 +12789,45 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditCompareStrings) {
 }
 
 
+// Restarts a call frame and completely drops all frames above.
+// Returns true if successful. Otherwise returns undefined or an error message.
+RUNTIME_FUNCTION(MaybeObject*, Runtime_LiveEditRestartFrame) {
+  HandleScope scope(isolate);
+  ASSERT(args.length() == 2);
+
+  // Check arguments.
+  Object* check;
+  { MaybeObject* maybe_check = Runtime_CheckExecutionState(
+      RUNTIME_ARGUMENTS(isolate, args));
+    if (!maybe_check->ToObject(&check)) return maybe_check;
+  }
+  CONVERT_NUMBER_CHECKED(int, index, Int32, args[1]);
+  Heap* heap = isolate->heap();
+
+  // Find the relevant frame with the requested index.
+  StackFrame::Id id = isolate->debug()->break_frame_id();
+  if (id == StackFrame::NO_ID) {
+    // If there are no JavaScript stack frames return undefined.
+    return heap->undefined_value();
+  }
+
+  int count = 0;
+  JavaScriptFrameIterator it(isolate, id);
+  for (; !it.done(); it.Advance()) {
+    if (index < count + it.frame()->GetInlineCount()) break;
+    count += it.frame()->GetInlineCount();
+  }
+  if (it.done()) return heap->undefined_value();
+
+  const char* error_message =
+      LiveEdit::RestartFrame(it.frame(), isolate->zone());
+  if (error_message) {
+    return *(isolate->factory()->LookupAsciiSymbol(error_message));
+  }
+  return heap->true_value();
+}
+
+
 // A testing entry. Returns statement position which is the closest to
 // source_position.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_GetFunctionCodePositionFromSource) {