Backed out changeset bdab19ff2fef (bug 1415485) for letting web platform tests in /css/CSS2/backgrounds/ frequently fail. r=backout a=backout

gfx/thebes/gfxPrefs.h

@@ -644,7 +644,7 @@ private:
   DECL_GFX_PREF(Live, "layout.css.touch_action.enabled",       TouchActionEnabled, bool, false);
 
   DECL_GFX_PREF(Live, "layout.display-list.build-twice",       LayoutDisplayListBuildTwice, bool, false);
-  DECL_GFX_PREF(Live, "layout.display-list.retain",            LayoutRetainDisplayList, bool, true);
+  DECL_GFX_PREF(Once, "layout.display-list.retain",            LayoutRetainDisplayList, bool, true);
   DECL_GFX_PREF(Live, "layout.display-list.rebuild-frame-limit", LayoutRebuildFrameLimit, uint32_t, 500);
   DECL_GFX_PREF(Live, "layout.display-list.dump",              LayoutDumpDisplayList, bool, false);
   DECL_GFX_PREF(Live, "layout.display-list.dump-content",      LayoutDumpDisplayListContent, bool, false);

layout/base/nsLayoutUtils.cpp

@@ -3618,33 +3618,6 @@ nsLayoutUtils::AddExtraBackgroundItems(nsDisplayListBuilder& aBuilder,
   }
 }
 
-/**
- * Returns a retained display list builder for frame |aFrame|. If there is no
- * retained display list builder property set for the frame, and if the flag
- * |aRetainingEnabled| is true, a new retained display list builder is created,
- * stored as a property for the frame, and returned.
- */
-static RetainedDisplayListBuilder*
-GetOrCreateRetainedDisplayListBuilder(nsIFrame* aFrame, bool aRetainingEnabled,
-                                      bool aBuildCaret)
-{
-  RetainedDisplayListBuilder* retainedBuilder =
-    aFrame->GetProperty(RetainedDisplayListBuilder::Cached());
-
-  if (retainedBuilder) {
-    return retainedBuilder;
-  }
-
-  if (aRetainingEnabled) {
-    retainedBuilder =
-      new RetainedDisplayListBuilder(aFrame, nsDisplayListBuilderMode::PAINTING,
-                                     aBuildCaret);
-    aFrame->SetProperty(RetainedDisplayListBuilder::Cached(), retainedBuilder);
-  }
-
-  return retainedBuilder;
-}
-
 nsresult
 nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext, nsIFrame* aFrame,
                           const nsRegion& aDirtyRegion, nscolor aBackstop,
@@ -3681,28 +3654,31 @@ nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext, nsIFrame* aFrame,
 
   TimeStamp startBuildDisplayList = TimeStamp::Now();
 
-  const bool buildCaret = !(aFlags & PaintFrameFlags::PAINT_HIDE_CARET);
-  const bool isForPainting = (aFlags & PaintFrameFlags::PAINT_WIDGET_LAYERS) &&
-    aBuilderMode == nsDisplayListBuilderMode::PAINTING;
-
-  // Retained display list builder is currently only used for content processes.
-  const bool retainingEnabled = isForPainting &&
-    gfxPrefs::LayoutRetainDisplayList() && XRE_IsContentProcess();
-
-  RetainedDisplayListBuilder* retainedBuilder =
-    GetOrCreateRetainedDisplayListBuilder(aFrame, retainingEnabled, buildCaret);
-
-  // Only use the retained display list builder if the retaining is currently
-  // enabled. This check is needed because it is possible that the pref has been
-  // disabled after creating the retained display list builder.
-  const bool useRetainedBuilder = retainedBuilder && retainingEnabled;
-
   Maybe<nsDisplayListBuilder> nonRetainedBuilder;
   Maybe<nsDisplayList> nonRetainedList;
   nsDisplayListBuilder* builderPtr = nullptr;
   nsDisplayList* listPtr = nullptr;
+  RetainedDisplayListBuilder* retainedBuilder = nullptr;
 
-  if (useRetainedBuilder) {
+  const bool buildCaret = !(aFlags & PaintFrameFlags::PAINT_HIDE_CARET);
+
+  // Enable display list retaining if the pref is set and if we are in a
+  // content process.
+  const bool retainDisplayList =
+    gfxPrefs::LayoutRetainDisplayList() && XRE_IsContentProcess();
+
+  if (retainDisplayList &&
+      aBuilderMode == nsDisplayListBuilderMode::PAINTING &&
+      (aFlags & PaintFrameFlags::PAINT_WIDGET_LAYERS)) {
+    retainedBuilder = aFrame->GetProperty(RetainedDisplayListBuilder::Cached());
+
+    if (!retainedBuilder) {
+      retainedBuilder =
+        new RetainedDisplayListBuilder(aFrame, aBuilderMode, buildCaret);
+      aFrame->SetProperty(RetainedDisplayListBuilder::Cached(), retainedBuilder);
+    }
+
+    MOZ_ASSERT(retainedBuilder);
     builderPtr = retainedBuilder->Builder();
     listPtr = retainedBuilder->List();
   } else {
@@ -3711,16 +3687,6 @@ nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext, nsIFrame* aFrame,
     nonRetainedList.emplace();
     listPtr = nonRetainedList.ptr();
   }
-
-  // Retained builder exists, but display list retaining is disabled.
-  if (!useRetainedBuilder && retainedBuilder) {
-    // Clear the modified frames lists and frame properties.
-    retainedBuilder->ClearModifiedFrameProps();
-
-    // Clear the retained display list.
-    retainedBuilder->List()->DeleteAll(retainedBuilder->Builder());
-  }
-
   nsDisplayListBuilder& builder = *builderPtr;
   nsDisplayList& list = *listPtr;
 
@@ -3850,12 +3816,14 @@ nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext, nsIFrame* aFrame,
           builder.IsBuildingLayerEventRegions() &&
           nsLayoutUtils::HasDocumentLevelListenersForApzAwareEvents(presShell));
 
+      const bool paintedPreviously =
+        aFrame->HasProperty(nsIFrame::ModifiedFrameList());
+
       // Attempt to do a partial build and merge into the existing list.
       // This calls BuildDisplayListForStacking context on a subset of the
       // viewport.
       bool merged = false;
-
-      if (useRetainedBuilder) {
+      if (retainedBuilder && paintedPreviously) {
         merged = retainedBuilder->AttemptPartialUpdate(aBackstop);
       }
 
@@ -4089,11 +4057,12 @@ nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext, nsIFrame* aFrame,
     AUTO_PROFILER_TRACING("Paint", "DisplayListResources");
 
     // Flush the list so we don't trigger the IsEmpty-on-destruction assertion
-    if (!useRetainedBuilder) {
+    if (!retainedBuilder) {
       list.DeleteAll(&builder);
-    }
-
       builder.EndFrame();
+    } else {
+      builder.EndFrame();
+    }
   }
   return NS_OK;
 }

layout/generic/nsFrame.cpp

@@ -1052,6 +1052,14 @@ nsIFrame::MarkNeedsDisplayItemRebuild()
 
   modifiedFrames->AppendElement(this);
 
+  // TODO: this is a bit of a hack. We are using ModifiedFrameList property to
+  // decide whether we are trying to reuse the display list.
+  if (displayRoot != rootFrame &&
+      !displayRoot->HasProperty(nsIFrame::ModifiedFrameList())) {
+    displayRoot->SetProperty(nsIFrame::ModifiedFrameList(),
+                             new nsTArray<nsIFrame*>());
+  }
+
   MOZ_ASSERT(PresContext()->LayoutPhaseCount(eLayoutPhase_DisplayListBuilding) == 0);
   SetFrameIsModified(true);
 

layout/painting/RetainedDisplayListBuilder.cpp

@@ -792,15 +792,6 @@ ClearFrameProps(nsTArray<nsIFrame*>& aFrames)
   }
 }
 
-void
-RetainedDisplayListBuilder::ClearModifiedFrameProps()
-{
-  nsTArray<nsIFrame*> modifiedFrames =
-    GetModifiedFrames(mBuilder.RootReferenceFrame());
-
-  ClearFrameProps(modifiedFrames);
-}
-
 bool
 RetainedDisplayListBuilder::AttemptPartialUpdate(nscolor aBackstop)
 {

layout/painting/RetainedDisplayListBuilder.h

@@ -27,14 +27,6 @@ struct RetainedDisplayListBuilder {
 
   bool AttemptPartialUpdate(nscolor aBackstop);
 
-  /**
-   * Iterates through the display list builder reference frame document and
-   * subdocuments, and clears the modified frame lists from the root frames.
-   * Also clears the frame properties set by RetainedDisplayListBuilder for all
-   * the frames in the modified frame lists.
-   */
-  void ClearModifiedFrameProps();
-
   NS_DECLARE_FRAME_PROPERTY_DELETABLE(Cached, RetainedDisplayListBuilder)
 
 private: