Do not slice classNames and classNameBindings speculatively.

packages/ember-glimmer/tests/integration/components/class-bindings-test.js

@@ -300,7 +300,7 @@ moduleFor('ClassNameBindings integration', class extends RenderingTest {
       init() {
         this._super();
 
-        let bindings = this.classNameBindings;
+        let bindings = this.classNameBindings = this.classNameBindings.slice();
 
         if (this.get('bindIsEnabled')) {
           bindings.push('isEnabled:enabled');

packages/ember-glimmer/tests/integration/components/curly-components-test.js

@@ -340,6 +340,7 @@ moduleFor('Components test: curly components', class extends RenderingTest {
     let FooBarComponent = Component.extend({
       init() {
         this._super();
+        this.classNames = this.classNames.slice();
         this.classNames.push('foo', 'bar', `outside-${this.get('extraClass')}`);
       }
     });

packages/ember-metal/lib/mixin.js

@@ -143,20 +143,32 @@ function giveMethodSuper(obj, key, method, values, descs) {
 
 function applyConcatenatedProperties(obj, key, value, values) {
   let baseValue = values[key] || obj[key];
+  let ret;
 
   if (baseValue) {
     if ('function' === typeof baseValue.concat) {
       if (value === null || value === undefined) {
-        return baseValue;
+        ret = baseValue;
       } else {
-        return baseValue.concat(value);
+        ret = baseValue.concat(value);
       }
     } else {
-      return makeArray(baseValue).concat(value);
+      ret = makeArray(baseValue).concat(value);
     }
   } else {
-    return makeArray(value);
+    ret = makeArray(value);
   }
+
+  runInDebug(() => {
+    // it is possible to use concatenatedProperties with strings (which cannot be frozen)
+    // only freeze objects...
+    if (typeof ret === 'object' && ret !== null) {
+      // prevent mutating `concatenatedProperties` array after it is applied
+      Object.freeze(ret);
+    }
+  });
+
+  return ret;
 }
 
 function applyMergedProperties(obj, key, value, values) {

packages/ember-routing/lib/utils.js

@@ -130,11 +130,7 @@ export function calculateCacheKey(prefix, _parts, values) {
   'Array of fully defined objects' style.
 */
 export function normalizeControllerQueryParams(queryParams) {
-  if (queryParams._qpMap) {
-    return queryParams._qpMap;
-  }
-
-  let qpMap = queryParams._qpMap = {};
+  let qpMap = {};
 
   for (let i = 0; i < queryParams.length; ++i) {
     accumulateQueryParamDescriptors(queryParams[i], qpMap);

packages/ember-routing/tests/utils_test.js

@@ -5,15 +5,6 @@ import {
 
 QUnit.module('Routing query parameter utils - normalizeControllerQueryParams');
 
-QUnit.test('returns the cached value if that has been previously set', function(assert) {
-  let cached = {};
-  let params = ['foo'];
-  params._qpMap = cached;
-
-  let normalized = normalizeControllerQueryParams(params);
-  equal(cached, normalized, 'cached value returned if previously set');
-});
-
 QUnit.test('converts array style into verbose object style', function(assert) {
   let paramName = 'foo';
   let params = [paramName];

packages/ember-views/lib/mixins/class_names_support.js

@@ -22,10 +22,7 @@ export default Mixin.create({
     this._super(...arguments);
 
     assert(`Only arrays are allowed for 'classNameBindings'`, Array.isArray(this.classNameBindings));
-    this.classNameBindings = this.classNameBindings.slice();
-
     assert(`Only arrays of static class strings are allowed for 'classNames'. For dynamic classes, use 'classNameBindings'.`, Array.isArray(this.classNames));
-    this.classNames = this.classNames.slice();
   },
 
   /**