Fix observable array access when formatting stack trace.

src/js/messages.js

Index: src/js/messages.js
diff --git a/src/js/messages.js b/src/js/messages.js
index 439043f809c5b50151c3313ed8e6b88e9e484d11..24d8d2bfa188bf3544e03083597e1dd7edd8ea2d 100644
--- a/src/js/messages.js
+++ b/src/js/messages.js
@@ -530,13 +530,15 @@ function FormatErrorString(error) {
 
 
 function GetStackFrames(raw_stack) {
+  var internal_raw_stack = new InternalArray();
+  %MoveArrayContents(raw_stack, internal_raw_stack);
   var frames = new InternalArray();
-  var sloppy_frames = raw_stack[0];
-  for (var i = 1; i < raw_stack.length; i += 4) {
-    var recv = raw_stack[i];
-    var fun = raw_stack[i + 1];
-    var code = raw_stack[i + 2];
-    var pc = raw_stack[i + 3];
+  var sloppy_frames = internal_raw_stack[0];
+  for (var i = 1; i < internal_raw_stack.length; i += 4) {
+    var recv = internal_raw_stack[i];
+    var fun = internal_raw_stack[i + 1];
+    var code = internal_raw_stack[i + 2];
+    var pc = internal_raw_stack[i + 3];
     // For traps in wasm, the bytecode offset is passed as (-1 - offset).
     // Otherwise, lookup the position from the pc.
     var pos = IS_NUMBER(fun) && pc < 0 ? (-1 - pc) :