Change corresponding bugs of LayoutTests leaks (ShadowDOM/Editing, context menu, drag).

Some tests in 364395 (context menu) look like 364417 (ShadowDOM/Editing).
Others look like 364392 (drag).

Only editing/context-menu-leak-document.html looks like
context menu, but it's not found in buildbot results.

BUG=364392,364395,364417,377615
NOTRY=True

Review URL: https://codereview.chromium.org/302693002

git-svn-id: svn://svn.chromium.org/blink/trunk@174834 bbb929c8-8fbe-4397-9dbb-9b2b20218538