Update target manager getter in isPrimaryPageFrame().

Also added a general unit test case for the function.

Bug:493046293
Change-Id: Iaad34d1b963d4beece476b8be8b3ca7a9977c372
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7744902
Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>

Author: yulunz

front_end/core/sdk/ResourceTreeModel.test.ts

@@ -131,6 +131,18 @@ describeWithMockConnection('ResourceTreeModel', () => {
     assert.isFalse(getResourceTreeModel(subframeTarget).mainFrame!.isOutermostFrame());
   });
 
+  it('identifies primary frame', async () => {
+    const tabTarget = createTarget({type: SDK.Target.Type.TAB});
+    const mainFrameTarget = createTarget({parentTarget: tabTarget});
+    const subframeTarget = createTarget({parentTarget: mainFrameTarget});
+
+    navigate(getMainFrame(mainFrameTarget));
+    navigate(getMainFrame(subframeTarget), {parentId: MAIN_FRAME_ID, id: 'child' as Protocol.Page.FrameId});
+
+    assert.isTrue(getResourceTreeModel(mainFrameTarget).mainFrame!.isPrimaryFrame());
+    assert.isFalse(getResourceTreeModel(subframeTarget).mainFrame!.isPrimaryFrame());
+  });
+
   it('emits PrimaryPageChanged event upon prerender activation', async () => {
     SDK.ChildTargetManager.ChildTargetManager.install();
     const tabTarget = createTarget({type: SDK.Target.Type.TAB});

front_end/core/sdk/ResourceTreeModel.ts

@@ -858,7 +858,8 @@ export class ResourceTreeFrame {
    * https://chromium.googlesource.com/chromium/src/+/HEAD/docs/frame_trees.md
    */
   isPrimaryFrame(): boolean {
-    return !this.#sameTargetParentFrame && this.#model.target() === TargetManager.instance().primaryPageTarget();
+    return !this.#sameTargetParentFrame &&
+        this.#model.target() === this.#model.target().targetManager().primaryPageTarget();
   }
 
   removeChildFrame(frame: ResourceTreeFrame, isSwap: boolean): void {