debug: Add verbose stacktrace function.

Zev and I found this useful for debugging what's happening inside
casperjs today.

(imported from commit 6fb42165c4ff138ba3417ac2ee0db92040e49fa4)

zephyr/static/js/debug.js

@@ -25,3 +25,48 @@ function print_elapsed_time(name, fun) {
     console.log(name + ': ' + (t1 - t0) + ' ms');
     return out;
 }
+
+// Javascript stack trac functionality, adapted from:
+// https://github.com/eriwen/javascript-stacktrace/blob/master/stacktrace.js
+// The first function is just a helper.
+function stringifyArguments(args) {
+    var i, result = [];
+    var slice = Array.prototype.slice;
+    for (i = 0; i < args.length; ++i) {
+        var arg = args[i];
+        if (arg === undefined) {
+            result[i] = 'undefined';
+        } else if (arg === null) {
+            result[i] = 'null';
+        } else if (arg.constructor) {
+            if (arg.constructor === Array) {
+                if (arg.length < 3) {
+                    result[i] = '[' + stringifyArguments(arg) + ']';
+                } else {
+                    result[i] = '[' + stringifyArguments(slice.call(arg, 0, 1)) + '...' + stringifyArguments(slice.call(arg, -1)) + ']';
+                }
+            } else if (arg.constructor === Object) {
+                result[i] = '#object';
+            } else if (arg.constructor === Function) {
+                result[i] = '#function';
+            } else if (arg.constructor === String) {
+                result[i] = '"' + arg + '"';
+            } else if (arg.constructor === Number) {
+                result[i] = arg;
+            }
+        }
+    }
+    return result.join(',');
+}
+
+// Usage: console.log(verbose_stacktrace(arguments.callee));
+function verbose_stacktrace(curr) {
+    var ANON = '{anonymous}', fnRE = /function\s*([\w\-$]+)?\s*\(/i, stack = [], fn, args, maxStackSize = 50;
+    while (curr && curr['arguments'] && stack.length < maxStackSize) {
+        fn = curr.toString();
+        args = Array.prototype.slice.call(curr['arguments'] || []);
+        stack[stack.length] = fn + '(' + stringifyArguments(args) + ')';
+        curr = curr.caller;
+    }
+    return stack;
+}