refactor(cdk/testing): reuse stabilize callback when creating test element

Any time we were creating a new test element, we were giving it a new stabilization callback. These changes reuse the same one between all elements in order to reduce the amount of memory for each element.

Author: crisbeto

src/cdk/testing/selenium-webdriver/selenium-web-driver-harness-environment.ts

@@ -74,6 +74,9 @@ export class SeleniumWebDriverHarnessEnvironment extends HarnessEnvironment<
   /** The options for this environment. */
   private _options: WebDriverHarnessEnvironmentOptions;
 
+  /** Environment stabilization callback passed to the created test elements. */
+  private _stabilizeCallback = () => this.forceStabilize();
+
   protected constructor(
     rawRootElement: () => webdriver.WebElement,
     options?: WebDriverHarnessEnvironmentOptions,
@@ -123,7 +126,7 @@ export class SeleniumWebDriverHarnessEnvironment extends HarnessEnvironment<
 
   /** Creates a `TestElement` from a raw element. */
   protected createTestElement(element: () => webdriver.WebElement): TestElement {
-    return new SeleniumWebDriverElement(element, () => this.forceStabilize());
+    return new SeleniumWebDriverElement(element, this._stabilizeCallback);
   }
 
   /** Creates a `HarnessLoader` rooted at the given raw element. */

src/cdk/testing/testbed/testbed-harness-environment.ts

@@ -96,6 +96,9 @@ export class TestbedHarnessEnvironment extends HarnessEnvironment<Element> {
   /** The options for this environment. */
   private _options: TestbedHarnessEnvironmentOptions;
 
+  /** Environment stabilization callback passed to the created test elements. */
+  private _stabilizeCallback = () => this.forceStabilize();
+
   protected constructor(
     rawRootElement: Element,
     private _fixture: ComponentFixture<unknown>,
@@ -198,7 +201,7 @@ export class TestbedHarnessEnvironment extends HarnessEnvironment<Element> {
 
   /** Creates a `TestElement` from a raw element. */
   protected createTestElement(element: Element): TestElement {
-    return new UnitTestElement(element, () => this.forceStabilize());
+    return new UnitTestElement(element, this._stabilizeCallback);
   }
 
   /** Creates a `HarnessLoader` rooted at the given raw element. */