Bug 1614233. Properly clip nsDisplayRemote. r=mattwoodrow

The existing code just clipped to a rect. We need to do the same clipping that the non-remote code path does which also handles border radius.

The existing code is the from initial implementation of nsDisplayRemote in https://hg.mozilla.org/mozilla-central/rev/85d06279c8358a8e1c883aa670a20212b1039a90 so I suspect that clipping to the inner view bounds instead of the frame content box is not an important difference.

Differential Revision: https://phabricator.services.mozilla.com/D62180

--HG--
extra : moz-landing-system : lando

layout/generic/nsSubDocumentFrame.cpp

@@ -361,10 +361,7 @@ void nsSubDocumentFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
     // We're the subdoc for <browser remote="true"> and it has
     // painted content.  Display its shadow layer tree.
     DisplayListClipState::AutoSaveRestore clipState(aBuilder);
-
+    clipState.ClipContainingBlockDescendantsToContentBox(aBuilder, this);
-    nsPoint offset = aBuilder->ToReferenceFrame(this);
-    nsRect bounds = this->EnsureInnerView()->GetBounds() + offset;
-    clipState.ClipContentDescendants(bounds);
 
     aLists.Content()->AppendNewToTop<nsDisplayRemote>(aBuilder, this);
     return;

layout/reftests/border-radius/reftest.list

@@ -84,7 +84,7 @@ fuzzy-if(/^Windows\x20NT\x2010\.0/.test(http.oscpu),0-35,0-194) == transforms-1.
 
 == zero-radius-clip-1.html zero-radius-clip-ref.html
 
-fails-if(browserIsFission) == iframe-1.html iframe-1-ref.html
+random-if(browserIsFission) == iframe-1.html iframe-1-ref.html
 
 # Test for antialiasing gaps between background and border
 fuzzy-if(gtkWidget,0-1,0-9) fuzzy-if(winWidget&&!d2d,0-1,0-9) fuzzy-if(d2d,0-5,0-40) fuzzy-if(Android||skiaContent,0-1,0-9) == curved-border-background-nogap.html curved-border-background-nogap-ref.html