fix($timeout): throw when trying to cancel non-$timeout promise

Previously, calling `$timeout.cancel()` with a promise that was not
generated by a call to `$timeout()` would do nothing. This could, for
example, happen when calling `.then()`/`.catch()` on the returned
promise, which creates a new promise, and passing that to
`$timeout.cancel()`.
With this commit, `$timeout.cancel()` will throw an error if called with
a non-$timeout promise, thus surfacing errors that would otherwise go
unnoticed.

Fixes #16424

BREAKING CHNAGE:

`$timeout.cancel()` will throw an error if called with a promise that
was not generated by `$timeout()`. Previously, it would silently do
nothing.

Before:
```js
var promise = $timeout(doSomething, 1000).then(doSomethingElse);
$timeout.cancel(promise);  // No error; timeout NOT canceled.
```

After:
```js
var promise = $timeout(doSomething, 1000).then(doSomethingElse);
$timeout.cancel(promise);  // Throws error.
```

Correct usage:
```js
var promise = $timeout(doSomething, 1000);
var newPromise = promise.then(doSomethingElse);
$timeout.cancel(promise);  // Timeout canceled.
```

docs/content/error/$timeout/badprom.ngdoc

@@ -0,0 +1,25 @@
+@ngdoc error
+@name $timeout:badprom
+@fullName Non-$timeout promise
+@description
+
+This error occurs when calling {@link ng.$timeout#cancel $timeout.cancel()} with a promise that
+was not generated by the {@link ng.$timeout $timeout} service. This can, for example, happen when
+calling {@link ng.$q#the-promise-api then()/catch()} on the returned promise, which creates a new
+promise, and pass that new promise to {@link ng.$timeout#cancel $timeout.cancel()}.
+
+Example of incorrect usage that leads to this error:
+
+```js
+var promise = $timeout(doSomething, 1000).then(doSomethingElse);
+$timeout.cancel(promise);
+```
+
+To fix the example above, keep a reference to the promise returned by
+{@link ng.$timeout $timeout()} and pass that to {@link ng.$timeout#cancel $timeout.cancel()}:
+
+```js
+var promise = $timeout(doSomething, 1000);
+var newPromise = promise.then(doSomethingElse);
+$timeout.cancel(promise);
+```

src/ng/timeout.js

@@ -1,5 +1,7 @@
 'use strict';
 
+var $timeoutMinErr = minErr('$timeout');
+
 /** @this */
 function $TimeoutProvider() {
   this.$get = ['$rootScope', '$browser', '$q', '$$q', '$exceptionHandler',
@@ -83,14 +85,24 @@ function $TimeoutProvider() {
      *   canceled.
      */
     timeout.cancel = function(promise) {
-      if (promise && promise.$$timeoutId in deferreds) {
-        // Timeout cancels should not report an unhandled promise.
-        markQExceptionHandled(deferreds[promise.$$timeoutId].promise);
-        deferreds[promise.$$timeoutId].reject('canceled');
-        delete deferreds[promise.$$timeoutId];
-        return $browser.defer.cancel(promise.$$timeoutId);
+      if (!promise) return false;
+
+      if (!promise.hasOwnProperty('$$timeoutId')) {
+        throw $timeoutMinErr('badprom',
+            '`$timeout.cancel()` called with a promise that was not generated by `$timeout()`.');
       }
-      return false;
+
+      if (!deferreds.hasOwnProperty(promise.$$timeoutId)) return false;
+
+      var id = promise.$$timeoutId;
+      var deferred = deferreds[id];
+
+      // Timeout cancels should not report an unhandled promise.
+      markQExceptionHandled(deferred.promise);
+      deferred.reject('canceled');
+      delete deferreds[id];
+
+      return $browser.defer.cancel(id);
     };
 
     return timeout;

test/ng/timeoutSpec.js

@@ -280,11 +280,17 @@ describe('$timeout', function() {
     }));
 
 
-    it('should not throw a runtime exception when given an undefined promise', inject(function($timeout) {
+    it('should not throw an error when given an undefined promise', inject(function($timeout) {
       expect($timeout.cancel()).toBe(false);
     }));
 
 
+    it('should throw an error when given a non-$timeout promise', inject(function($timeout) {
+      var promise = $timeout(noop).then(noop);
+      expect(function() { $timeout.cancel(promise); }).toThrowMinErr('$timeout', 'badprom');
+    }));
+
+
     it('should forget references to relevant deferred', inject(function($timeout, $browser) {
       // $browser.defer.cancel is only called on cancel if the deferred object is still referenced
       var cancelSpy = spyOn($browser.defer, 'cancel').and.callThrough();