Fixes all tests and add feature control for ParentNode.replaceChildren.

In this CL, fixes all the remaining tests for ParentNode.replaceChildren
by following the steps outlined in the spec[1]. Also connected
RuntimeEnabledFeature to blink::feature so it's finch controllable.

[1] https://dom.spec.whatwg.org/#dom-parentnode-replacechildren

Bug: 1067384
Change-Id: I246b96d8907c222d15bc80376d83a0bc5ff90e34
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2270678
Reviewed-by: Chris Harrelson <[email protected]>
Reviewed-by: Mason Freed <[email protected]>
Commit-Queue: Yu Han <[email protected]>
Cr-Commit-Position: refs/heads/master@{#786490}
diff --git a/third_party/blink/common/features.cc b/third_party/blink/common/features.cc
index 0258e28..d16f165 100644
--- a/third_party/blink/common/features.cc
+++ b/third_party/blink/common/features.cc
@@ -101,6 +101,9 @@
 #endif
 };
 
+const base::Feature kParentNodeReplaceChildren {
+  "ParentNodeReplaceChildren", base::FEATURE_ENABLED_BY_DEFAULT};
+
 // Enable browser-initiated dedicated worker script loading
 // (PlzDedicatedWorker). https://crbug.com/906991
 const base::Feature kPlzDedicatedWorker{"PlzDedicatedWorker",