Enable support for display:contents.

Intent-to-ship thread:

https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/XzdNrEvn4Qk/650SpqXTBAAJ

Bug: 657748
Change-Id: I01a7804d2214ac19fb8f58e1f68c23957cf071f7
Reviewed-on: https://chromium-review.googlesource.com/848920
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526971}
diff --git a/third_party/WebKit/Source/platform/runtime_enabled_features.json5 b/third_party/WebKit/Source/platform/runtime_enabled_features.json5
index 9a7b0a3..ec61d3e 100644
--- a/third_party/WebKit/Source/platform/runtime_enabled_features.json5
+++ b/third_party/WebKit/Source/platform/runtime_enabled_features.json5
@@ -219,7 +219,7 @@
     },
     {
       name: "CSSDisplayContents",
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "CSSFontSizeAdjust",