Mark two virtual/android tests as Slow for causing flaky timeouts

virtual/android/url-bar/bottom-fixed-adjusted-when-showing-url-bar.html
and virtual/android/fullscreen/video-scrolled-iframe.html are causing
flaky timeouts.

TBR=nator@chromiun.org

Bug: 1049138
No-Try: true
Change-Id: If30b1c39d7b73354e782458c924708bc820934c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2039143Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738592}

third_party/blink/web_tests/SlowTests

@@ -677,3 +677,6 @@ crbug.com/1048204 external/wpt/selection/idlharness.window.html [ Slow ]
 # Reaching the stack size limit makes for a consistently slow test with
 # occasional timeouts on Win7
 crbug.com/937546 [ Win7 ] http/tests/security/xss-DENIED-cross-origin-stack-overflow.html [ Slow ]
+
+crbug.com/1049138 virtual/android/url-bar/bottom-fixed-adjusted-when-showing-url-bar.html [ Slow ]
+crbug.com/1049138 virtual/android/fullscreen/video-scrolled-iframe.html [ Slow ]