Sheriff: disable flaky media tests

No change to production logic. This disables two tests which are flaking
on the bf cache bot.

Tbr: mlamouri@chromium.org
Bug: 1157320
Test: None
Change-Id: Ie6c76747f1b468fd30dac4a792b2bf287bade88c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2582835Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835508}

content/public/android/javatests/src/org/chromium/content/browser/MediaSessionTest.java

@@ -336,6 +336,7 @@ public class MediaSessionTest {
     @Test
     @SmallTest
     @Feature({"MediaSession"})
+    @DisabledTest(message = "https://crbug.com/1157320")
     public void testShortVideoStopsIfLostFocus() throws Exception {
         Assert.assertEquals(
                 AudioManager.AUDIOFOCUS_LOSS, mAudioFocusChangeListener.getAudioFocusState());
@@ -448,6 +449,7 @@ public class MediaSessionTest {
     @MediumTest
     @Feature({"MediaSession"})
     @Restriction(Restriction.RESTRICTION_TYPE_NON_LOW_END_DEVICE) // crbug.com/589176
+    @DisabledTest(message = "https://crbug.com/1157320")
     public void testMediaResumeAfterTransientFocusLoss() throws Exception {
         Assert.assertEquals(
                 AudioManager.AUDIOFOCUS_LOSS, mAudioFocusChangeListener.getAudioFocusState());