[SPInvalidation] Handle pixel-snapping of paint invalidation rects

third_party/WebKit/Source/core/paint/BoxPaintInvalidator.cpp

Index: third_party/WebKit/Source/core/paint/BoxPaintInvalidator.cpp
diff --git a/third_party/WebKit/Source/core/paint/BoxPaintInvalidator.cpp b/third_party/WebKit/Source/core/paint/BoxPaintInvalidator.cpp
index f813347b85cce652662f1f1a2eaadc35f60fc2a0..14a155c34efc0fb52ab3b22bad9d1ad8b9137e71 100644
--- a/third_party/WebKit/Source/core/paint/BoxPaintInvalidator.cpp
+++ b/third_party/WebKit/Source/core/paint/BoxPaintInvalidator.cpp
@@ -157,17 +157,27 @@ PaintInvalidationReason BoxPaintInvalidator::computePaintInvalidationReason() {
       return reason;
   }
 
-  // If the transform is not identity or translation, incremental invalidation
-  // is not applicable because the difference between oldBounds and newBounds
-  // doesn't cover all area needing invalidation.
-  // FIXME: Should also consider ancestor transforms since
-  // paintInvalidationContainer. crbug.com/426111.
   if (reason == PaintInvalidationIncremental &&
-      m_context.oldBounds != m_context.newBounds &&
-      m_context.paintInvalidationContainer != m_box && m_box.hasLayer() &&
-      m_box.layer()->transform() &&
-      !m_box.layer()->transform()->isIdentityOrTranslation())
-    return PaintInvalidationBoundsChange;
+      m_context.oldBounds != m_context.newBounds) {
+    if (m_context.newBoundsCoversExtraPixels ||
+        m_context.oldBoundsCoversExtraPixels) {
+      // Incremental invalidation is not applicable because the difference
+      // between oldBounds and newBounds may not cover all changed pixels along
+      // the edges.
+      return PaintInvalidationBoundsChange;
+    }
+
+    // If the transform is not identity or translation, incremental invalidation
+    // is not applicable because the difference between oldBounds and newBounds
+    // doesn't cover all area needing invalidation.
+    // TODO(crbug.com/426111): Should also consider ancestor transforms
+    // since paintInvalidationContainer. Combine this logic into the above
+    // boundsCoversExtraPixels logic.
+    if (m_context.paintInvalidationContainer != m_box && m_box.hasLayer() &&
+        m_box.layer()->transform() &&
+        !m_box.layer()->transform()->isIdentityOrTranslation())
+      return PaintInvalidationBoundsChange;
+  }
 
   const ComputedStyle& style = m_box.styleRef();
   if (style.backgroundLayers().thisOrNextLayersUseContentBox() ||