Backed out changeset 919de32d4905 (bug 1525134) for build bustages. CLOSED TREE

layout/base/nsCSSFrameConstructor.cpp

@@ -2336,6 +2336,9 @@ nsIFrame* nsCSSFrameConstructor::ConstructDocElementFrame(
     return nullptr;
   }
 
+  // Make sure to start any background image loads for the root element now.
+  computedStyle->StartBackgroundImageLoads();
+
   nsFrameConstructorSaveState docElementContainingBlockAbsoluteSaveState;
   if (mHasRootAbsPosContainingBlock) {
     // Push the absolute containing block now so we can absolutely position
@@ -5647,6 +5650,10 @@ void nsCSSFrameConstructor::ConstructFramesFromItem(
     return;
   }
 
+  // Start background loads during frame construction so that we're
+  // guaranteed that they will be started before onload fires.
+  computedStyle->StartBackgroundImageLoads();
+
   AutoRestore<nsFrameState> savedStateBits(aState.mAdditionalStateBits);
   if (item.mIsGeneratedContent) {
     // Ensure that frames created here are all tagged with