Revert "refactor: use isObservable provided by rxjs 6.1+ (#27668)"

This reverts commit 7e6350ce2e.

packages/core/test/util/lang_spec.ts

@@ -5,7 +5,8 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-import {isPromise} from '@angular/core/src/util/lang';
+import {isObservable, isPromise} from '@angular/core/src/util/lang';
+import {of } from 'rxjs';
 
 {
   describe('isPromise', () => {
@@ -25,4 +26,22 @@ import {isPromise} from '@angular/core/src/util/lang';
       expect(isPromise(null)).toEqual(false);
     });
   });
+
+  describe('isObservable', () => {
+    it('should be true for an Observable', () => expect(isObservable(of (true))).toEqual(true));
+
+    it('should be true if the argument is the object with subscribe function',
+       () => expect(isObservable({subscribe: () => {}})).toEqual(true));
+
+    it('should be false if the argument is undefined',
+       () => expect(isObservable(undefined)).toEqual(false));
+
+    it('should be false if the argument is null', () => expect(isObservable(null)).toEqual(false));
+
+    it('should be false if the argument is an object',
+       () => expect(isObservable({})).toEqual(false));
+
+    it('should be false if the argument is a function',
+       () => expect(isObservable(() => {})).toEqual(false));
+  });
 }

packages/core/test/view/BUILD.bazel

@@ -17,7 +17,6 @@ ts_library(
         "//packages/core/testing",
         "//packages/platform-browser",
         "//packages/private/testing",
-        "@npm//rxjs",
     ],
 )
 

packages/core/test/view/provider_spec.ts

@@ -6,7 +6,6 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Observable} from 'rxjs';
 import {AfterContentChecked, AfterContentInit, AfterViewChecked, AfterViewInit, ChangeDetectorRef, DoCheck, ElementRef, ErrorHandler, EventEmitter, Injector, OnChanges, OnDestroy, OnInit, Renderer2, SimpleChange, TemplateRef, ViewContainerRef,} from '@angular/core';
 import {getDebugContext} from '@angular/core/src/errors';
 import {ArgumentType, DepFlags, NodeFlags, Services, anchorDef, asElementData, directiveDef, elementDef, providerDef, textDef} from '@angular/core/src/view/index';
@@ -342,11 +341,13 @@ import {ARG_TYPE_VALUES, checkNodeInlineOrDynamic, createRootView, createAndGetR
         let unsubscribeSpy: any;
 
         class SomeService {
-          emitter = new Observable((callback: any) => {
-            const subscription = emitter.subscribe(callback);
-            unsubscribeSpy = spyOn(subscription, 'unsubscribe').and.callThrough();
-            return subscription;
-          });
+          emitter = {
+            subscribe: (callback: any) => {
+              const subscription = emitter.subscribe(callback);
+              unsubscribeSpy = spyOn(subscription, 'unsubscribe').and.callThrough();
+              return subscription;
+            }
+          };
         }
 
         const handleEvent = jasmine.createSpy('handleEvent');