Re-enable .../off-main-thread/.../close-code-and-reason.html

Layout test
virtual/off-main-thread-websocket/http/tests/websocket/close-code-and-reason.html
was flaky with early versions of the off-main-thread WebSocket
implementation. It is no longer flaky, and this virtual test suite has
been switched to running the old "on main thread" WebSocket
implementation. So the flaky expectation is no longer needed. Remove it.

Bug: 831320
Change-Id: I6bb6b2430dbc0fbfad3c5e4ca629487cffaac7a3
Reviewed-on: https://chromium-review.googlesource.com/1036765Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557096}

third_party/WebKit/LayoutTests/TestExpectations

@@ -2774,9 +2774,6 @@ crbug.com/803200 external/wpt/websockets/cookies/006.html?wss [ Failure ]
 crbug.com/803200 external/wpt/websockets/opening-handshake/005.html?wss [ Pass Failure ]
 crbug.com/803200 virtual/off-main-thread-websocket/external/wpt/websockets/cookies/006.html?wss [ Failure ]
 crbug.com/803200 virtual/off-main-thread-websocket/external/wpt/websockets/opening-handshake/005.html?wss [ Pass Failure ]
-# These tests are failing because of experimental off-main-thread WebSocket
-# implementation.
-crbug.com/831320 virtual/off-main-thread-websocket/http/tests/websocket/close-code-and-reason.html [ Pass Failure ]
 
 crbug.com/805463 external/wpt/acid/acid3/numbered-tests.html [ Skip ]