Turn on render throttling for iframes with pending sheets.

third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in

Index: third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in
diff --git a/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in b/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in
index 7aedeaabe8cb2454702f867a0f3b22739748c00b..3854e78409f7ccd5e2c95581c3dcc5ee39b63967 100644
--- a/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in
+++ b/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in
@@ -187,6 +187,7 @@ ReducedReferrerGranularity
 ReloadwithoutSubResourceCacheRevalidation
 RemotePlayback status=experimental
 RenderingPipelineThrottling status=stable
+RenderingPipelineThrottlingLoadingIframes status=experimental

[ojan, 2016/11/08 21:27:06]

I'd just mark this as status=stable from the beginning. We just need the flag so
we have an easy way to turn it off in case it breaks content.

[esprehn, 2016/11/08 22:18:35]

I'm going to land as experimental now while I wait on the Intent thread so this
doesn't rot as we discussed over chat. I'll land a stable flip later this week.
:)

 RenderUnicodeControlCharacters status=stable
 ResizeObserver status=experimental
 // Handles frame scrolling via the root PaintLayer instead of the FrameView.