Sheriff: mark 3 tests as flaky on Linux

- virtual/android/rootscroller/nested-rootscroller-browser-controls-bounds-shown.html,
- virtual/android/url-bar/bottom-fixed-adjusted-when-showing-url-bar.html, and
- virtual/threaded/animations/responsive/viewport-unit-translate-responsive.html

TBR=joedow
NOTRY=true

Bug: 805794
Change-Id: Id7710e3d04f23d84ab289669c588f6c486803b71
Reviewed-on: https://chromium-review.googlesource.com/885667
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Reviewed-by: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/master@{#531835}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3385,3 +3385,9 @@ crbug.com/803449 http/tests/devtools/sources/debugger-breakpoints/breakpoints-ui
 # Flaking on linux_chromium_rel_ng
 crbug.com/804709 [ Linux ] virtual/gpu/fast/canvas/canvas-fillPath-shadow.html [ Pass Failure ]
 crbug.com/805788 [ Linux Win7 Win10 ] virtual/threaded/animations/responsive/viewport-unit-transform-responsive.html [ Pass Timeout ]
+
+# Sheriff failures 2018-01-25
+# Flaking on Linux Tests, WebKit Linux Trusty (also ASAN, Leak)
+crbug.com/805794 [ Linux ] virtual/android/rootscroller/nested-rootscroller-browser-controls-bounds-shown.html [ Pass Failure ]
+crbug.com/805794 [ Linux ] virtual/android/url-bar/bottom-fixed-adjusted-when-showing-url-bar.html [ Pass Failure ]
+crbug.com/805794 [ Linux ] virtual/threaded/animations/responsive/viewport-unit-translate-responsive.html [ Pass Timeout ]