Bug 1496194 - Ensure the inner sticky rect stays inside the outer sticky rect. r=botond

Depends on D15136

Differential Revision: https://phabricator.services.mozilla.com/D15137

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

gfx/tests/crashtests/1496194.html

@@ -0,0 +1,14 @@
+<style>
+/*
+ AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+ AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+ AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+ */
+* {
+ position: sticky;
+ padding-right: 1px;
+ left: 2px;
+ right: 163px;
+ display: ruby-base;
+}
+</style>

gfx/tests/crashtests/crashtests.list

@@ -177,3 +177,4 @@ load 1505426-1.html
 load 1508811.html
 load 1508822.html
 load 1509099.html
+load 1496194.html

layout/generic/StickyScrollContainer.cpp

@@ -320,6 +320,12 @@ void StickyScrollContainer::GetScrollRanges(nsIFrame* aFrame,
   // Note that this doesn't necessarily solve all problems stemming from
   // comparing pre- and post-collapsing margins (TODO: find a proper solution).
   *aInner = aInner->Intersect(*aOuter);
+  if (aInner->IsEmpty()) {
+    // This might happen if aInner didn't intersect aOuter at all initially,
+    // in which case aInner is empty and outside aOuter. Make sure it doesn't
+    // extend outside aOuter.
+    *aInner = aInner->MoveInsideAndClamp(*aOuter);
+  }
 }
 
 void StickyScrollContainer::PositionContinuations(nsIFrame* aFrame) {