Separate clear stack and run it after each spec

[finishes #50197985][fix #109418332]
- Fixes #985
- Fixes #945
- Fixes #366

src/core/ClearStack.js

@@ -0,0 +1,36 @@
+getJasmineRequireObj().clearStack = function(j$) {
+  function messageChannelImpl(global) {
+    var channel = new global.MessageChannel(),
+        head = {},
+        tail = head;
+
+    channel.port1.onmessage = function() {
+      head = head.next;
+      var task = head.task;
+      delete head.task;
+      task();
+    };
+
+    return function clearStack(fn) {
+      tail = tail.next = { task: fn };
+      channel.port2.postMessage(0);
+    };
+  }
+
+  function getClearStack(global) {
+    if (global && global.process && j$.isFunction_(global.process.nextTick)) {
+      return global.process.nextTick;
+    } else if (j$.isFunction_(global.setImmediate)) {
+      return global.setImmediate;
+    } else if (!j$.util.isUndefined(global.MessageChannel)) {
+      return messageChannelImpl(global);
+    } else if (j$.isFunction_(global.setTimeout)) {
+      var realSetTimeout = global.setTimeout;
+      return function clearStack(fn) {
+        realSetTimeout(fn, 0);
+      }
+    }
+  }
+
+  return getClearStack;
+};