Split-out change for https://codereview.chromium.org/1145993002/ patch set 11

Source/core/layout/LayoutBox.cpp

Index: Source/core/layout/LayoutBox.cpp
diff --git a/Source/core/layout/LayoutBox.cpp b/Source/core/layout/LayoutBox.cpp
index 32f145224f98f089742fad77885151311c8d025a..6f6ad20081f9adc363a66f834ccfaa6c949777fc 100644
--- a/Source/core/layout/LayoutBox.cpp
+++ b/Source/core/layout/LayoutBox.cpp
@@ -166,16 +166,6 @@ void LayoutBox::styleWillChange(StyleDifference diff, const ComputedStyle& newSt
 {
     const ComputedStyle* oldStyle = style();
     if (oldStyle) {
-        // The background of the root element or the body element could propagate up to
-        // the canvas. Just dirty the entire canvas when our style changes substantially.
-        if ((diff.needsPaintInvalidation() || diff.needsLayout()) && node()
-            && (isHTMLHtmlElement(*node()) || isHTMLBodyElement(*node()))) {
-            view()->setShouldDoFullPaintInvalidation();
-
-            if (oldStyle->hasEntirelyFixedBackground() != newStyle.hasEntirelyFixedBackground())
-                view()->compositor()->setNeedsUpdateFixedBackground();
-        }
-
         // When a layout hint happens and an object's position style changes, we have to do a layout
         // to dirty the layout tree using the old position value now.
         if (diff.needsFullLayout() && parent() && oldStyle->position() != newStyle.position()) {
@@ -3925,7 +3915,8 @@ PaintInvalidationReason LayoutBox::paintInvalidationReason(const LayoutBoxModelO
         && hasLayer() && layer()->transform() && !layer()->transform()->isIdentityOrTranslation())
         return PaintInvalidationBoundsChange;
 
-    if (!style()->hasBackground() && !style()->hasBoxDecorations()) {
+    bool paintsBackground = style()->hasBackground() && !isDocumentElement() && !backgroundStolenForBeingBody();
+    if (!paintsBackground && !style()->hasBoxDecorations()) {
         // We could let incremental invalidation cover non-composited scrollbars, but just
         // do a full invalidation because incremental invalidation will go away with slimming paint.
         if (invalidationReason == PaintInvalidationIncremental && hasNonCompositedScrollbars())
@@ -3933,18 +3924,26 @@ PaintInvalidationReason LayoutBox::paintInvalidationReason(const LayoutBoxModelO
         return invalidationReason;
     }
 
-    if (style()->backgroundLayers().thisOrNextLayersUseContentBox() || style()->maskLayers().thisOrNextLayersUseContentBox()) {
+    if (paintsBackground && (style()->backgroundLayers().thisOrNextLayersUseContentBox() || style()->maskLayers().thisOrNextLayersUseContentBox())) {
         LayoutRect oldContentBoxRect = m_rareData ? m_rareData->m_previousContentBoxRect : LayoutRect();
         LayoutRect newContentBoxRect = contentBoxRect();
         if (oldContentBoxRect != newContentBoxRect)
             return PaintInvalidationContentBoxChange;
     }
 
-    if (style()->backgroundLayers().thisOrNextLayersHaveLocalAttachment()) {
+    if (paintsBackground && style()->backgroundLayers().thisOrNextLayersHaveLocalAttachment()) {
         LayoutRect oldLayoutOverflowRect = m_rareData ? m_rareData->m_previousLayoutOverflowRect : LayoutRect();
         LayoutRect newLayoutOverflowRect = layoutOverflowRect();
-        if (oldLayoutOverflowRect != newLayoutOverflowRect)
-            return PaintInvalidationLayoutOverflowBoxChange;
+        if (oldLayoutOverflowRect != newLayoutOverflowRect) {
+            // Background positioning for the LayoutView are based on the box of the root element.
+            // Whether full invalidation is needed will be checked with special logic in
+            // LayoutView::invalidatePaintIfNeeded. Here we only need to guarantee incremental
+            // painting is done for newly expanded area.
+            if (!isLayoutView())
+                return PaintInvalidationLayoutOverflowBoxChange;
+            if (invalidationReason < PaintInvalidationIncremental)
+                invalidationReason = PaintInvalidationIncremental;
+        }
     }
 
     LayoutSize oldBorderBoxSize = computePreviousBorderBoxSize(oldBounds.size());
@@ -3969,11 +3968,13 @@ PaintInvalidationReason LayoutBox::paintInvalidationReason(const LayoutBoxModelO
             return PaintInvalidationBorderBoxChange;
     }
 
+    if (!paintsBackground)
+        return invalidationReason;
+
     if (oldBorderBoxSize.width() != newBorderBoxSize.width() && mustInvalidateBackgroundOrBorderPaintOnWidthChange())
         return PaintInvalidationBorderBoxChange;
     if (oldBorderBoxSize.height() != newBorderBoxSize.height() && mustInvalidateBackgroundOrBorderPaintOnHeightChange())
         return PaintInvalidationBorderBoxChange;
-
     return PaintInvalidationIncremental;
 }
 
@@ -4684,7 +4685,7 @@ void LayoutBox::logicalExtentAfterUpdatingLogicalWidth(const LayoutUnit& newLogi
     setMarginRight(oldMarginRight);
 }
 
-inline bool LayoutBox::mustInvalidateFillLayersPaintOnWidthChange(const FillLayer& layer) const
+bool LayoutBox::mustInvalidateFillLayersPaintOnWidthChange(const FillLayer& layer) const
 {
     // Nobody will use multiple layers without wanting fancy positioning.
     if (layer.next())