HParams: Bug Fix - Ensure context menu always opens within the window (#6474)

## Motivation for features / changes
It was possible to open a context menu which would overflow the page.
This actually lead to a strange CLS issue which looked pretty bad. Now
the custom_modal component will check the size of the content once it
has rendered and adjust its position to ensure it fits in the page.

## Screenshots of UI changes (or N/A)
The context menu never overflows the window

![35353f79-2987-455b-af30-d05e1e29cefa](https://github.com/tensorflow/tensorboard/assets/78179109/aa44934c-7d51-4154-9e83-33b67d8e01b3)

This also works at the bottom of the page but it doesn't come across as
well in a screenshot

![image](https://github.com/tensorflow/tensorboard/assets/78179109/0158dbbf-2507-4ed9-92ca-a4293f94887d)

Author: rileyajones

tensorboard/webapp/widgets/custom_modal/custom_modal_component.ts

@@ -69,6 +69,7 @@ export class CustomModalComponent implements OnInit {
       // Wait until after the next browser frame.
       window.requestAnimationFrame(() => {
         if (visible) {
+          this.ensureContentIsWithinWindow();
           this.onOpen.emit();
         } else {
           this.onClose.emit();
@@ -90,6 +91,29 @@ export class CustomModalComponent implements OnInit {
     document.addEventListener('click', this.clickListener);
   }
 
+  private ensureContentIsWithinWindow() {
+    if (!this.content) {
+      return;
+    }
+
+    const boundingBox = this.content.nativeElement.getBoundingClientRect();
+    if (boundingBox.left < 0) {
+      this.content.nativeElement.style.left = 0;
+    }
+    if (boundingBox.left + boundingBox.width > window.innerWidth) {
+      this.content.nativeElement.style.left =
+        window.innerWidth - boundingBox.width + 'px';
+    }
+
+    if (boundingBox.top < 0) {
+      this.content.nativeElement.style.top = 0;
+    }
+    if (boundingBox.top + boundingBox.height > window.innerHeight) {
+      this.content.nativeElement.style.top =
+        window.innerHeight - boundingBox.height + 'px';
+    }
+  }
+
   @HostListener('document:keydown.escape', ['$event'])
   public close() {
     document.removeEventListener('click', this.clickListener);

tensorboard/webapp/widgets/custom_modal/custom_modal_test.ts

@@ -13,6 +13,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 ==============================================================================*/
 import {ComponentFixture, TestBed} from '@angular/core/testing';
+import {By} from '@angular/platform-browser';
 import {CustomModalComponent} from './custom_modal_component';
 import {CommonModule} from '@angular/common';
 import {
@@ -135,4 +136,59 @@ describe('custom modal', () => {
       expect(fixture.componentInstance.isOpen).toBeFalse();
     });
   });
+
+  describe('ensures content is always within the window', () => {
+    beforeEach(() => {
+      window.innerHeight = 1000;
+      window.innerWidth = 1000;
+    });
+
+    it('sets left to 0 if less than 0', async () => {
+      const fixture = TestBed.createComponent(TestableComponent);
+      fixture.detectChanges();
+      fixture.componentInstance.openAtPosition({x: -10, y: 0});
+      expect(fixture.componentInstance.isOpen).toBeFalse();
+      await waitFrame();
+      fixture.detectChanges();
+
+      const content = fixture.debugElement.query(By.css('.content'));
+      expect(content.nativeElement.style.left).toEqual('0px');
+    });
+
+    it('sets top to 0 if less than 0', async () => {
+      const fixture = TestBed.createComponent(TestableComponent);
+      fixture.detectChanges();
+      fixture.componentInstance.openAtPosition({x: 0, y: -10});
+      expect(fixture.componentInstance.isOpen).toBeFalse();
+      await waitFrame();
+      fixture.detectChanges();
+
+      const content = fixture.debugElement.query(By.css('.content'));
+      expect(content.nativeElement.style.top).toEqual('0px');
+    });
+
+    it('sets left to maximum if content overflows the window', async () => {
+      const fixture = TestBed.createComponent(TestableComponent);
+      fixture.detectChanges();
+      fixture.componentInstance.openAtPosition({x: 1010, y: 0});
+      expect(fixture.componentInstance.isOpen).toBeFalse();
+      await waitFrame();
+      fixture.detectChanges();
+      const content = fixture.debugElement.query(By.css('.content'));
+      // While rendering in a test the elements width and height will appear to be 0.
+      expect(content.nativeElement.style.left).toEqual('1000px');
+    });
+
+    it('sets top to maximum if content overflows the window', async () => {
+      const fixture = TestBed.createComponent(TestableComponent);
+      fixture.detectChanges();
+      fixture.componentInstance.openAtPosition({x: 0, y: 1010});
+      expect(fixture.componentInstance.isOpen).toBeFalse();
+      await waitFrame();
+      fixture.detectChanges();
+      const content = fixture.debugElement.query(By.css('.content'));
+      // While rendering in a test the elements width and height will appear to be 0.
+      expect(content.nativeElement.style.top).toEqual('1000px');
+    });
+  });
 });