Disable unit test failing on L

TouchActionTest.Pan will start failing upstream as soon as
L bots are added.

BUG=412145

Review URL: https://codereview.chromium.org/557953002

Cr-Commit-Position: refs/heads/master@{#294191}

build/android/pylib/gtest/filter/webkit_unit_tests_disabled

@@ -23,3 +23,6 @@ DeferredImageDecoderTest.drawIntoSkPictureProgressive
 
 # crbug.com/320005
 CoreAnimationCompositorAnimationsTest.ConvertTimingForCompositorIterationCount
+
+# crbug.com/412145
+TouchActionTest.Pan