Disable flaky ScreenshotTabObserverTest tests.

TBR=petewil@chromium.org, jianli@chromium.org, dtrainor@chromium.org, isherman@chromium.org
NOTRY=True

Bug: 901856
Change-Id: I61b14dca18356bb71618150795cddc7cce016574
Reviewed-on: https://chromium-review.googlesource.com/c/1318911Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605659}

chrome/android/javatests/src/org/chromium/chrome/browser/feature_engagement/ScreenshotTabObserverTest.java

@@ -57,8 +57,10 @@ public class ScreenshotTabObserverTest {
         });
     }
 
+    // Disabled due to flakiness. https://crbug.com/901856
     @Test
     @SmallTest
+    @DisabledTest
     public void testScreenshotNumberReportingOne() {
         MetricsUtils.HistogramDelta histogramDeltaZeroScreenshots =
                 new MetricsUtils.HistogramDelta("Tab.Screenshot.ScreenshotsPerPage", 0);
@@ -77,8 +79,10 @@ public class ScreenshotTabObserverTest {
                 histogramDeltaTwoScreenshots.getDelta());
     }
 
+    // Disabled due to flakiness. https://crbug.com/901856
     @Test
     @SmallTest
+    @DisabledTest
     public void testScreenshotNumberReportingTwo() {
         MetricsUtils.HistogramDelta histogramDeltaTwoScreenshots =
                 new MetricsUtils.HistogramDelta("Tab.Screenshot.ScreenshotsPerPage", 2);
@@ -89,8 +93,10 @@ public class ScreenshotTabObserverTest {
                 histogramDeltaTwoScreenshots.getDelta());
     }
 
+    // Disabled due to flakiness. https://crbug.com/901856
     @Test
     @SmallTest
+    @DisabledTest
     public void testScreenshotActionReporting() {
         MetricsUtils.HistogramDelta histogramDeltaScreenshotNoAction =
                 new MetricsUtils.HistogramDelta("Tab.Screenshot.Action", 0);