Add two tests to LeakExpectations

These were exposed by leak detector change, dgozman@ is going to fix them.

Bug: 833609
Change-Id: I068afd816b67158a0d1ee5aef515525685398069
Reviewed-on: https://chromium-review.googlesource.com/1014462
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551135}

third_party/WebKit/LayoutTests/LeakExpectations

@@ -56,6 +56,12 @@ crbug.com/765721 [ Linux ] virtual/stable/http/tests/navigation/navigation-inter
 crbug.com/809609 [ Linux ] editing/pasteboard/drop-file-svg.html [ Pass Leak ]
 crbug.com/809609 [ Linux ] editing/inserting/insert_div_with_style.html [ Pass Leak ]
 
+# -----------------------------------------------------------------
+# Not reverted by dgozman@ request, exposed by leak detector change.
+# -----------------------------------------------------------------
+crbug.com/833609 http/tests/history/back-during-beforeunload.html [ Leak Pass ]
+crbug.com/833609 fast/forms/form-associated-element-crash2.html [ Leak Pass ]
+
 # -----------------------------------------------------------------
 # Sheriff 2018-03-08
 # -----------------------------------------------------------------