fix($mdInteraction): clean up events on $rootScope destroy (#11641)

this prevents unit tests from leaking memory

Fixes: #11493

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## PR Checklist
Please check that your PR fulfills the following requirements:
- [x] The commit message follows [our guidelines](https://github.com/angular/material/blob/master/.github/CONTRIBUTING.md#-commit-message-format)
- [ ] Tests for the changes have been added or this is not a bug fix / enhancement
- [ ] Docs have been added, updated, or were not required

## PR Type
What kind of change does this PR introduce?
<!-- Please check the one that applies to this PR using "x". -->
```
[x] Bugfix
[ ] Enhancement
[ ] Documentation content changes
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Infrastructure changes
[ ] Other... Please describe:
```

## What is the current behavior?

Currently the $mdInteraction service registers when invoked. This causes a memory leak in unit tests because nothing is in place to clean up the events.

<!-- Please describe the current behavior that you are modifying and link to one or more relevant issues. -->
Issue Number: #11493

## What is the new behavior?

Now on the $destroy event of rootScope the events registered will be unregistered.

## Does this PR introduce a breaking change?
```
[ ] Yes
[x] No
```
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## Other information

src/core/services/interaction/interaction.js

@@ -33,15 +33,20 @@ angular
  * </hljs>
  *
  */
-function MdInteractionService($timeout, $mdUtil) {
+function MdInteractionService($timeout, $mdUtil, $rootScope) {
   this.$timeout = $timeout;
   this.$mdUtil = $mdUtil;
+  this.$rootScope = $rootScope;
 
+  // IE browsers can also trigger pointer events, which also leads to an interaction.
+  this.pointerEvent = 'MSPointerEvent' in window ? 'MSPointerDown' : 'PointerEvent' in window ? 'pointerdown' : null;
   this.bodyElement = angular.element(document.body);
   this.isBuffering = false;
   this.bufferTimeout = null;
   this.lastInteractionType = null;
   this.lastInteractionTime = null;
+  this.inputHandler = this.onInputEvent.bind(this);
+  this.bufferedInputHandler = this.onBufferInputEvent.bind(this);
 
   // Type Mappings for the different events
   // There will be three three interaction types
@@ -65,24 +70,41 @@ function MdInteractionService($timeout, $mdUtil) {
   };
 
   this.initializeEvents();
+  this.$rootScope.$on('$destroy', this.deregister.bind(this));
 }
 
+/**
+ * Removes all event listeners created by $mdInteration on the
+ * body element.
+ */
+MdInteractionService.prototype.deregister = function() {
+
+    this.bodyElement.off('keydown mousedown', this.inputHandler);
+
+    if ('ontouchstart' in document.documentElement) {
+      this.bodyElement.off('touchstart', this.bufferedInputHandler);
+    }
+
+    if (this.pointerEvent) {
+      this.bodyElement.off(this.pointerEvent, this.inputHandler);
+    }
+
+};
+
 /**
  * Initializes the interaction service, by registering all interaction events to the
  * body element.
  */
 MdInteractionService.prototype.initializeEvents = function() {
-  // IE browsers can also trigger pointer events, which also leads to an interaction.
-  var pointerEvent = 'MSPointerEvent' in window ? 'MSPointerDown' : 'PointerEvent' in window ? 'pointerdown' : null;
 
-  this.bodyElement.on('keydown mousedown', this.onInputEvent.bind(this));
+  this.bodyElement.on('keydown mousedown', this.inputHandler);
 
   if ('ontouchstart' in document.documentElement) {
-    this.bodyElement.on('touchstart', this.onBufferInputEvent.bind(this));
+    this.bodyElement.on('touchstart', this.bufferedInputHandler);
   }
 
-  if (pointerEvent) {
-    this.bodyElement.on(pointerEvent, this.onInputEvent.bind(this));
+  if (this.pointerEvent) {
+    this.bodyElement.on(this.pointerEvent, this.inputHandler);
   }
 
 };

src/core/services/interaction/interaction.spec.js

@@ -1,12 +1,16 @@
 describe("$mdInteraction service", function() {
 
   var $mdInteraction = null;
+  var $rootScope = null;
   var bodyElement = null;
+  var $timeout = null;
 
   beforeEach(module('material.core'));
 
   beforeEach(inject(function($injector) {
     $mdInteraction = $injector.get('$mdInteraction');
+    $rootScope = $injector.get('$rootScope');
+    $timeout = $injector.get('$timeout');
 
     bodyElement = angular.element(document.body);
   }));
@@ -75,4 +79,38 @@ describe("$mdInteraction service", function() {
 
   });
 
-});
+  describe('when $rootScope is destroyed', function () {
+
+    var _initialTouchStartEvent = document.documentElement.ontouchstart;
+
+    beforeAll(function () {
+      document.documentElement.ontouchstart = function () {};
+    });
+
+    beforeEach(function () {
+      $mdInteraction.lastInteractionType = 'initial';
+      $rootScope.$destroy();
+    });
+
+    afterAll(function () {
+      document.documentElement.ontouchstart = _initialTouchStartEvent;
+    });
+
+    it('should remove mousedown events', function () {
+      bodyElement.triggerHandler('mousedown');
+      expect($mdInteraction.getLastInteractionType()).toEqual('initial');
+    });
+
+    it('should remove keydown events', function () {
+      bodyElement.triggerHandler('keydown');
+      expect($mdInteraction.getLastInteractionType()).toEqual('initial');
+    });
+
+    it('should remove touchstart events', function () {
+      bodyElement.triggerHandler('touchstart');
+      expect($mdInteraction.getLastInteractionType()).toEqual('initial');
+    });
+
+  });
+
+});