test: Wait a bit after switching to "mobile" for some metrics pixels

test/verify/check-metrics

@@ -277,7 +277,18 @@ class TestHistoryMetrics(testlib.MachineCase):
         b.wait_in_text("#metrics-hour-1597662000000:not(.metrics-hour-compressed) .metrics-events-hour-header-expanded .spikes_count", "3 spikes")
         b.wait_in_text("#metrics-hour-1597662000000:not(.metrics-hour-compressed) .metrics-events-hour-header-expanded .spikes_info", "1 Memory, 1 Disk I/O, 1 Network I/O")
 
-        b.assert_pixels(".metrics", "metrics-history-expanded-hour", ignore=[".spikes_count"])
+        # There is something really funny going on with the navigation
+        # bar in the mobile layout; it sometimes appears in a random
+        # position in the screenshot. We fix that by adding an extra
+        # delay after switching to "mobile".
+
+        b.assert_pixels(".metrics", "metrics-history-expanded-hour", ignore=[".spikes_count"],
+                        skip_layouts=["mobile"])
+        b.set_layout("mobile")
+        time.sleep(1.0)
+        b.assert_pixels_in_current_layout(".metrics", "metrics-history-expanded-hour",
+                                          ignore=[".spikes_count"])
+        b.set_layout("desktop")
 
         b.click("#metrics-hour-1597662000000 button.metrics-events-expander")
         b.wait_in_text("#metrics-hour-1597662000000.metrics-hour-compressed", "1:00")