Bug 1340958 - Do not call EffectCompositor::GetServoAnimationRule for print preview. r=heycam

The only one caller of GetServoAnimationRule is Gecko_GetAnimationRule.
There is no risk that pres context is destroyed in Gecko_GetAnimationRule.

MozReview-Commit-ID: 52pxbCiCNoJ

--HG--
extra : rebase_source : 8000e267d1d5706c709f807e11396dda3579c4dc

dom/animation/EffectCompositor.cpp

@@ -482,10 +482,8 @@ EffectCompositor::GetServoAnimationRule(const dom::Element* aElement,
                                         CSSPseudoElementType aPseudoType,
                                         CascadeLevel aCascadeLevel)
 {
-  if (!mPresContext || !mPresContext->IsDynamic()) {
-    // For print or print preview, ignore animations.
-    return nullptr;
-  }
+  MOZ_ASSERT(mPresContext && mPresContext->IsDynamic(),
+             "Should not be in print preview");
 
   EffectSet* effectSet = EffectSet::GetEffectSet(aElement, aPseudoType);
   if (!effectSet) {

layout/style/ServoBindings.cpp

@@ -404,7 +404,8 @@ Gecko_GetAnimationRule(RawGeckoElementBorrowed aElement,
     return emptyDeclarationBlock;
   }
   nsPresContext* presContext = doc->GetShell()->GetPresContext();
-  if (!presContext) {
+  if (!presContext || !presContext->IsDynamic()) {
+    // For print or print preview, ignore animations.
     return emptyDeclarationBlock;
   }