update-w3c-deps adds "-webkit-" to CSS properties which Blink has only prefixed one. We can avoid this by implementing unprefixed properties in a runtime flag enabled only in layout test.
Here is the list of such CSS properties at this moment. However, they don't appear in web-platform-tests.
app-region
appearance
border-after
border-after-color
border-after-style
border-after-width
border-before
border-before-color
border-before-style
border-before-width
border-end
border-end-color
border-end-style
border-end-width
border-horizontal-spacing
border-start
border-start-color
border-start-style
border-start-width
border-vertical-spacing
box-align
box-decoration-break
box-direction
box-flex
box-flex-group
box-lines
box-ordinal-group
box-orient
box-pack
box-reflect
column-break-after
column-break-before
column-break-inside
font-size-delta
font-smoothing
highlight
hyphenate-character
line-break
line-clamp
locale
logical-height
logical-width
margin-after
margin-after-collapse
margin-before
margin-before-collapse
margin-bottom-collapse
margin-collapse
margin-end
margin-start
margin-top-collapse
mask-box-image
mask-box-image-outset
mask-box-image-repeat
mask-box-image-slice
mask-box-image-source
mask-box-image-width
mask-clip
mask-composite
mask-image
mask-origin
mask-position
mask-position-x
mask-position-y
mask-repeat
mask-repeat-x
mask-repeat-y
mask-size
max-logical-height
max-logical-width
min-logical-height
min-logical-width
padding-after
padding-before
padding-end
padding-start
perspective-origin-x
perspective-origin-y
print-color-adjust
rtl-ordering
ruby-position
tap-highlight-color
text-combine
text-decorations-in-effect
text-emphasis
text-emphasis-color
text-emphasis-position
text-emphasis-style
text-fill-color
text-security
text-stroke
text-stroke-color
text-stroke-width
transform-origin-x
transform-origin-y
transform-origin-z
user-drag
user-modify
user-select
Comment 1 by tkent@chromium.org
, May 26 2016