Disable 2 layout tests after r548309 and add a TODO to reenable them

BUG=787020
TBR=eae

Change-Id: I9931e0f0c73a6a0bb7dbade9c8c189acec1cb9d2
Reviewed-on: https://chromium-review.googlesource.com/997174Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548331}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3995,6 +3995,10 @@ crbug.com/827209 virtual/mouseevent_fractional/fast/events/middleClickAutoscroll
 # Utility for manual testing, not intended to be run as part of layout tests.
 crbug.com/785955 http/tests/credentialmanager/tools/virtual-authenticator-environment-manual.html [ Skip ]
 
+# Disabled after r548309.  TODO(thomasanderson): Reenable these tests
+crbug.com/787020 virtual/gpu/fast/canvas/canvas-zero-length-lineCap.html [ Pass Failure ]
+crbug.com/787020 virtual/threaded/http/tests/devtools/tracing/timeline-js/compile-script.js [ Pass Failure ]
+
 # These Web Authentication API would require either real hardware, or
 # virtual simulation thereof (work in progress, see: https://crbug.com/785955).
 crbug.com/826936 external/wpt/webauthn/createcredential-badargs-authnrselection.https.html [ Pass Timeout ]