Mark dom-storage-open.js timeout on Win7

TBR=chenwilliam@chromium.org
NOTRY=true

Bug: 799164
Change-Id: I6f264e8e99d472398368151b9f10349f7b3cbe8f
Reviewed-on: https://chromium-review.googlesource.com/850636Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527077}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3557,3 +3557,4 @@ crbug.com/798592 [ Win7 ] virtual/threaded/http/tests/devtools/tracing/timeline-
 crbug.com/798680 external/wpt/pointerevents/pointerlock/pointerevent_pointerlock_supercedes_capture-manual.html [ Pass Timeout ]
 crbug.com/799127 [ Mac ] external/wpt/resource-timing/test_resource_timing.html [ Failure ]
 crbug.com/799137 [ Mac ] virtual/modern-media-controls/media/controls/modern/doubletap-to-jump-backwards-at-start.html [ Pass Timeout ]
+crbug.com/799164 [ Win7 ] http/tests/devtools/startup/dom-storage-open.js [ Pass Timeout ]