Bug 1405359 - Add some logging code in ScrollingLayersHelper. r=jrmuizel

MozReview-Commit-ID: Lb4UeUxO5HL

--HG--
extra : rebase_source : e5e8c58380055693664bb1a5241bab4d803dfdab

gfx/layers/wr/ScrollingLayersHelper.cpp

@@ -12,6 +12,9 @@
 #include "nsDisplayList.h"
 #include "UnitTransforms.h"
 
+#define SLH_LOG(...)
+//#define SLH_LOG(...) printf_stderr("SLH: " __VA_ARGS__)
+
 namespace mozilla {
 namespace layers {
 
@@ -55,12 +58,15 @@ void
 ScrollingLayersHelper::BeginItem(nsDisplayItem* aItem,
                                  const StackingContextHelper& aStackingContext)
 {
+  SLH_LOG("processing item %p\n", aItem);
+
   ItemClips clips(aItem->GetActiveScrolledRoot(), aItem->GetClipChain());
   MOZ_ASSERT(!mItemClipStack.empty());
   if (clips.HasSameInputs(mItemClipStack.back())) {
     // Early-exit because if the clips are the same then we don't need to do
     // do the work of popping the old stuff and then pushing it right back on
     // for the new item.
+    SLH_LOG("early-exit for %p\n", aItem);
     return;
   }
   mItemClipStack.back().Unapply(mBuilder);
@@ -130,6 +136,8 @@ ScrollingLayersHelper::BeginItem(nsDisplayItem* aItem,
 
   clips.Apply(mBuilder);
   mItemClipStack.push_back(clips);
+
+  SLH_LOG("done setup for %p\n", aItem);
 }
 
 std::pair<Maybe<FrameMetrics::ViewID>, Maybe<wr::WrClipId>>