DCHECK that paint properties are never null

third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp

Index: third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
index 33b273b60daf80594f2ac0e0269b02351be61adc..1a64e54946f81f11bef07606ec7f56855b48b2ab 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
@@ -8,6 +8,12 @@
 
 namespace blink {
 
+#if DCHECK_IS_ON()
+static bool gNullPaintPropertyChecksDisabled = false;
+DisableNullPaintPropertyChecks::DisableNullPaintPropertyChecks()
+    : m_disabler(&gNullPaintPropertyChecksDisabled, true) {}
+#endif
+
 PaintChunker::PaintChunker() {}
 
 PaintChunker::~PaintChunker() {}
@@ -26,6 +32,19 @@ void PaintChunker::updateCurrentPaintChunkProperties(
 bool PaintChunker::incrementDisplayItemIndex(const DisplayItem& item) {
   DCHECK(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
 
+#if DCHECK_IS_ON()
+  if (!gNullPaintPropertyChecksDisabled) {
+    // Property nodes should never be null because they should either be set to
+    // properties created by a LayoutObject/FrameView, or be set to a non-null
+    // root node. If these DCHECKs are hit we are missing a call to update the
+    // properties. See: ScopedPaintChunkProperties.
+    DCHECK(m_currentProperties.transform);
+    DCHECK(m_currentProperties.clip);
+    DCHECK(m_currentProperties.effect);
+    DCHECK(m_currentProperties.scroll);
+  }
+#endif
+
   ItemBehavior behavior;
   Optional<PaintChunk::Id> newChunkId;
   if (DisplayItem::isForeignLayerType(item.getType())) {