Disable flaky unittests.

Bug: b/158617675
Test: manually.
Change-Id: Ibdb1b3bfdba72bb5eefbe1f841614e2fe3b10b2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2248924Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Meilin Wang <meilinw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779172}

ash/ambient/ui/photo_view_unittest.cc

@@ -12,9 +12,10 @@ namespace ash {
 
 using AmbientPhotoViewTest = AmbientAshTestBase;
 
+// TODO(b/158617675): test is flaky.
 // Test that image is scaled to fill full screen when image and display are in
 // the same orientation.
-TEST_F(AmbientPhotoViewTest, ShouldResizeImageToFillFullScreen) {
+TEST_F(AmbientPhotoViewTest, DISABLED_ShouldResizeImageToFillFullScreen) {
   // Start Ambient mode.
   ambient_controller()->Show();
   // Fastforward enough time to update the photo.
@@ -32,9 +33,11 @@ TEST_F(AmbientPhotoViewTest, ShouldResizeImageToFillFullScreen) {
   ambient_controller()->Destroy();
 }
 
+// TODO(b/158617675): test is flaky.
 // Test that image is scaled to fill one direction of the screen when image and
 // display are in different orientations.
-TEST_F(AmbientPhotoViewTest, ShouldResizeImageToFillOneDirectionOfScreen) {
+TEST_F(AmbientPhotoViewTest,
+       DISABLED_ShouldResizeImageToFillOneDirectionOfScreen) {
   // Start Ambient mode.
   ambient_controller()->Show();
   // Fastforward enough time to update the photo.