Bug 695763. Part 5. Invalidate background images if they are not decoded and we are asked to do a sync decode. r=matt.woodrow

layout/base/nsCSSRendering.cpp

@@ -3036,19 +3036,29 @@ nsCSSRendering::GetBackgroundLayerRect(nsPresContext* aPresContext,
   return state.mFillArea;
 }
 
+/* static */ bool
+nsCSSRendering::IsBackgroundImageDecodedForStyleContextAndLayer(
+  const nsStyleBackground *aBackground, uint32_t aLayer)
+{
+  const nsStyleImage* image = &aBackground->mLayers[aLayer].mImage;
+  if (image->GetType() == eStyleImageType_Image) {
+    nsCOMPtr<imgIContainer> img;
+    if (NS_SUCCEEDED(image->GetImageData()->GetImage(getter_AddRefs(img)))) {
+      if (!img->IsDecoded()) {
+        return false;
+      }
+    }
+  }
+  return true;
+}
+
 /* static */ bool
 nsCSSRendering::AreAllBackgroundImagesDecodedForFrame(nsIFrame* aFrame)
 {
   const nsStyleBackground *bg = aFrame->StyleContext()->StyleBackground();
   NS_FOR_VISIBLE_BACKGROUND_LAYERS_BACK_TO_FRONT(i, bg) {
-    const nsStyleImage* image = &bg->mLayers[i].mImage;
-    if (image->GetType() == eStyleImageType_Image) {
-      nsCOMPtr<imgIContainer> img;
-      if (NS_SUCCEEDED(image->GetImageData()->GetImage(getter_AddRefs(img)))) {
-        if (!img->IsDecoded()) {
-          return false;
-        }
-      }
+    if (!IsBackgroundImageDecodedForStyleContextAndLayer(bg, i)) {
+      return false;
     }
   }
   return true;

layout/base/nsCSSRendering.h

@@ -396,6 +396,12 @@ struct nsCSSRendering {
                                        const nsStyleBackground::Layer& aLayer,
                                        uint32_t aFlags);
 
+  /**
+   * Checks if image in layer aLayer of aBackground is currently decoded.
+   */
+  static bool IsBackgroundImageDecodedForStyleContextAndLayer(
+    const nsStyleBackground *aBackground, uint32_t aLayer);
+
   /**
    * Checks if all images that are part of the background for aFrame are
    * currently decoded.

layout/base/nsDisplayList.cpp

@@ -2193,6 +2193,12 @@ void nsDisplayBackgroundImage::ComputeInvalidationRegion(nsDisplayListBuilder* a
     aInvalidRegion->Or(bounds, geometry->mBounds);
     return;
   }
+  if (aBuilder->ShouldSyncDecodeImages()) {
+    if (mBackgroundStyle &&
+        !nsCSSRendering::IsBackgroundImageDecodedForStyleContextAndLayer(mBackgroundStyle, mLayer)) {
+      aInvalidRegion->Or(*aInvalidRegion, bounds);
+    }
+  }
   if (!bounds.IsEqualInterior(geometry->mBounds)) {
     // Positioning area is unchanged, so invalidate just the change in the
     // painting area.