Bug 962594 - Don't build CSS animations for elements that are in a display:none subtree. r=heycam

layout/base/RestyleManager.cpp

@@ -3025,11 +3025,18 @@ ElementRestyler::ComputeRestyleResultFromNewContext(nsIFrame* aSelf,
 
   if (oldContext->ShouldSuppressLineBreak() !=
         aNewContext->ShouldSuppressLineBreak()) {
-    LOG_RESTYLE_CONTINUE("NS_STYLE_SUPPRESS_LINEBREAK differes"
+    LOG_RESTYLE_CONTINUE("NS_STYLE_SUPPRESS_LINEBREAK differs"
                          "between old and new style contexts");
     return eRestyleResult_Continue;
   }
 
+  if (oldContext->IsInDisplayNoneSubtree() !=
+        aNewContext->IsInDisplayNoneSubtree()) {
+    LOG_RESTYLE_CONTINUE("NS_STYLE_IN_DISPLAY_NONE_SUBTREE differs between old"
+                         " and new style contexts");
+    return eRestyleResult_Continue;
+  }
+
   return eRestyleResult_Stop;
 }
 

layout/style/nsAnimationManager.cpp

@@ -266,7 +266,9 @@ nsAnimationManager::CheckAnimationRule(nsStyleContext* aStyleContext,
   // build the animations list
   dom::AnimationTimeline* timeline = aElement->OwnerDoc()->Timeline();
   AnimationPlayerPtrArray newPlayers;
-  BuildAnimations(aStyleContext, aElement, timeline, newPlayers);
+  if (!aStyleContext->IsInDisplayNoneSubtree()) {
+    BuildAnimations(aStyleContext, aElement, timeline, newPlayers);
+  }
 
   if (newPlayers.IsEmpty()) {
     if (collection) {

layout/style/nsStyleContext.cpp

@@ -299,6 +299,12 @@ nsStyleContext::MoveTo(nsStyleContext* aNewParent)
 {
   MOZ_ASSERT(aNewParent != mParent);
 
+  // This function shouldn't be getting called if the parents have different
+  // values for some flags in mBits, because if that were the case we would need
+  // to recompute those bits for |this|. (TODO: add more flags to |mask|.)
+  DebugOnly<uint64_t> mask = NS_STYLE_IN_DISPLAY_NONE_SUBTREE;
+  MOZ_ASSERT((mParent->mBits & mask) == (aNewParent->mBits & mask));
+
   // Assertions checking for visited style are just to avoid some tricky
   // cases we can't be bothered handling at the moment.
   MOZ_ASSERT(!IsStyleIfVisited());
@@ -688,6 +694,12 @@ nsStyleContext::ApplyStyleFixups(bool aSkipParentDisplayBasedStyleFixup)
     }
   }
 
+  // Set the NS_STYLE_IN_DISPLAY_NONE_SUBTREE bit
+  if ((mParent && mParent->IsInDisplayNoneSubtree()) ||
+      disp->mDisplay == NS_STYLE_DISPLAY_NONE) {
+    mBits |= NS_STYLE_IN_DISPLAY_NONE_SUBTREE;
+  }
+
   // Suppress border/padding of ruby level containers
   if (disp->mDisplay == NS_STYLE_DISPLAY_RUBY_BASE_CONTAINER ||
       disp->mDisplay == NS_STYLE_DISPLAY_RUBY_TEXT_CONTAINER) {

layout/style/nsStyleContext.h

@@ -160,6 +160,10 @@ public:
   bool ShouldSuppressLineBreak() const
     { return !!(mBits & NS_STYLE_SUPPRESS_LINEBREAK); }
 
+  // Does this style context or any of its ancestors have display:none set?
+  bool IsInDisplayNoneSubtree() const
+    { return !!(mBits & NS_STYLE_IN_DISPLAY_NONE_SUBTREE); }
+
   // Does this style context represent the style for a pseudo-element or
   // inherit data from such a style context?  Whether this returns true
   // is equivalent to whether it or any of its ancestors returns

layout/style/nsStyleStruct.h

@@ -58,8 +58,10 @@ class imgIContainer;
 #define NS_STYLE_IS_GOING_AWAY             0x040000000
 // See nsStyleContext::ShouldSuppressLineBreak
 #define NS_STYLE_SUPPRESS_LINEBREAK        0x080000000
+// See nsStyleContext::IsInDisplayNoneSubtree
+#define NS_STYLE_IN_DISPLAY_NONE_SUBTREE   0x100000000
 // See nsStyleContext::GetPseudoEnum
-#define NS_STYLE_CONTEXT_TYPE_SHIFT        32
+#define NS_STYLE_CONTEXT_TYPE_SHIFT        33
 
 // Additional bits for nsRuleNode's mDependentBits:
 #define NS_RULE_NODE_GC_MARK                0x02000000