Turning CSSScrollSnapPoints stable.

Intent-to-ship:
https://groups.google.com/a/chromium.org/d/topic/blink-dev/K4m85YRD1II/discussion

Bug: 497851
Change-Id: Iae62b81fda3b6dab683833d61937b8a4b134fb4a
Reviewed-on: https://chromium-review.googlesource.com/1110852Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Sandra Sun <sunyunjia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569664}

third_party/WebKit/LayoutTests/virtual/stable/webexposed/css-properties-as-js-properties-expected.txt

@@ -254,6 +254,31 @@ rowGap
 rx
 ry
 scrollBehavior
+scrollMargin
+scrollMarginBlock
+scrollMarginBlockEnd
+scrollMarginBlockStart
+scrollMarginBottom
+scrollMarginInline
+scrollMarginInlineEnd
+scrollMarginInlineStart
+scrollMarginLeft
+scrollMarginRight
+scrollMarginTop
+scrollPadding
+scrollPaddingBlock
+scrollPaddingBlockEnd
+scrollPaddingBlockStart
+scrollPaddingBottom
+scrollPaddingInline
+scrollPaddingInlineEnd
+scrollPaddingInlineStart
+scrollPaddingLeft
+scrollPaddingRight
+scrollPaddingTop
+scrollSnapAlign
+scrollSnapStop
+scrollSnapType
 setProperty
 shapeImageThreshold
 shapeMargin

third_party/WebKit/LayoutTests/virtual/stable/webexposed/css-property-listing-expected.txt

@@ -278,6 +278,25 @@ All changes to this list should go through Blink's feature review process: http:
     rx
     ry
     scroll-behavior
+    scroll-margin-block-end
+    scroll-margin-block-start
+    scroll-margin-bottom
+    scroll-margin-inline-end
+    scroll-margin-inline-start
+    scroll-margin-left
+    scroll-margin-right
+    scroll-margin-top
+    scroll-padding-block-end
+    scroll-padding-block-start
+    scroll-padding-bottom
+    scroll-padding-inline-end
+    scroll-padding-inline-start
+    scroll-padding-left
+    scroll-padding-right
+    scroll-padding-top
+    scroll-snap-align
+    scroll-snap-stop
+    scroll-snap-type
     shape-image-threshold
     shape-margin
     shape-outside
@@ -590,6 +609,28 @@ All changes to this list should go through Blink's feature review process: http:
     place-self
         align-self
         justify-self
+    scroll-margin
+        scroll-margin-bottom
+        scroll-margin-left
+        scroll-margin-right
+        scroll-margin-top
+    scroll-margin-block
+        scroll-margin-block-end
+        scroll-margin-block-start
+    scroll-margin-inline
+        scroll-margin-inline-end
+        scroll-margin-inline-start
+    scroll-padding
+        scroll-padding-bottom
+        scroll-padding-left
+        scroll-padding-right
+        scroll-padding-top
+    scroll-padding-block
+        scroll-padding-block-end
+        scroll-padding-block-start
+    scroll-padding-inline
+        scroll-padding-inline-end
+        scroll-padding-inline-start
     text-decoration
         text-decoration-color
         text-decoration-line

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -330,7 +330,7 @@
     },
     {
       name: "CSSScrollSnapPoints",
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "CSSSnapSize",