Mark external/wpt/beacon/headers/header-content-type.html as Slow

Bug: 779965, 626703, 729849
Change-Id: I795f9a2a22b886bc70301452adbab626ab324b99
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Reviewed-on: https://chromium-review.googlesource.com/746487
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512820}

third_party/WebKit/LayoutTests/FlagExpectations/enable-features=NetworkService

@@ -9,7 +9,6 @@ Bug(none) virtual/mojo-loading [ Skip ]
 
 Bug(none) external/wpt/clear-site-data/storage.https.html [ Failure ]
 Bug(none) external/wpt/XMLHttpRequest/overridemimetype-blob.html [ Failure ]
-Bug(none) external/wpt/beacon/headers/header-content-type.html [ Timeout ]
 Bug(none) external/wpt/clear-site-data/navigation.https.html [ Timeout ]
 Bug(none) external/wpt/content-security-policy/generic/filesystem-urls-match-filesystem.sub.html [ Failure ]
 Bug(none) external/wpt/content-security-policy/inside-worker/dedicated-inheritance.html [ Failure Timeout ]

third_party/WebKit/LayoutTests/SlowTests

@@ -493,3 +493,5 @@ crbug.com/626703 [ Debug ] external/wpt/html/nemantics/tabular-data/processing-m
 
 # This test continues to fail as timeout on Win7(dbg)
 crbug.com/757292 [ Win Debug ] external/wpt/encoding/legacy-mb-korean/euc-kr/euckr-encode-form-errors-han.html [ Slow ]
+
+crbug.com/779965 external/wpt/beacon/headers/header-content-type.html [ Slow ]

third_party/WebKit/LayoutTests/TestExpectations

@@ -1783,7 +1783,6 @@ crbug.com/626703 external/wpt/2dcontext/building-paths/canvas_complexshapes_bezi
 crbug.com/626703 external/wpt/beacon/beacon-cors.sub.window.html [ Timeout ]
 crbug.com/626703 external/wpt/beacon/beacon-navigate.html [ Timeout ]
 crbug.com/626703 external/wpt/beacon/beacon-redirect.window.html [ Timeout ]
-crbug.com/626703 external/wpt/beacon/headers/header-content-type.html [ Pass Timeout ]
 crbug.com/626703 external/wpt/compat/webkit-text-fill-color-property-005.html [ Failure ]
 crbug.com/626703 external/wpt/css/CSS2/text/text-align-white-space-003.xht [ Failure ]
 crbug.com/626703 external/wpt/css/CSS2/text/text-align-white-space-007.xht [ Failure ]