Add a feature for not compositing small scrollers

third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5

Index: third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
diff --git a/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5 b/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
index 2449ac00f49602b6de9743dd2ff7f2d6fcabb4b4..96a07827e5debdd6c35ace613a669efbb345db2a 100644
--- a/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
+++ b/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
@@ -691,6 +691,10 @@
     {
       name: "NewRemotePlaybackPipeline",
     },
+    {
+      name: "NotCompositeSmallScroller",

[flackr, 2017/06/05 17:50:41]

Suggestion, how about SkipCompositingSmallScrollers or
CompositeOnlyLargeScrollers?

[yigu, 2017/06/06 20:01:10]

Done.

+      status: "experimental",

[flackr, 2017/06/05 17:50:41]

I think status experimental means this would be enabled with
--experimental-web-platform-features which I don't think we should do until this
feature is implemented.

[yigu, 2017/06/06 20:01:10]

Have updated it to "test".

+    },
     {
       name: "NotificationBadge",
       status: "stable",