[css-tables] Clean up code that detects significant border changes

De-duplicate; narrow a condition; fix a method that did the opposite of
its name; add comments, etc.

No new tests because there _should_ be no behavior changes.

BUG=613728

Review-Url: https://codereview.chromium.org/2153283002
Cr-Commit-Position: refs/heads/master@{#406051}

third_party/WebKit/Source/core/layout/LayoutTableBoxComponent.cpp

@@ -4,6 +4,7 @@
 
 #include "core/layout/LayoutTableBoxComponent.h"
 
+#include "core/layout/LayoutTable.h"
 #include "core/style/ComputedStyle.h"
 
 namespace blink {
@@ -25,4 +26,13 @@ void LayoutTableBoxComponent::imageChanged(WrappedImagePtr, const IntRect*)
     m_backgroundChangedSinceLastPaintInvalidation = true;
 }
 
+bool LayoutTableBoxComponent::doCellsHaveDirtyWidth(const LayoutObject& tablePart, const LayoutTable& table, const StyleDifference& diff, const ComputedStyle& oldStyle)
+{
+    // ComputedStyle::diffNeedsFullLayoutAndPaintInvalidation sets needsFullLayout when border sizes
+    // change: checking diff.needsFullLayout() is an optimization, not required for correctness.
+    // TODO(dgrogan): Remove tablePart.needsLayout()? Perhaps it was an old optimization but now it
+    // seems that diff.needsFullLayout() implies tablePart.needsLayout().
+    return diff.needsFullLayout() && tablePart.needsLayout() && table.collapseBorders() && !oldStyle.border().sizeEquals(tablePart.style()->border());
+}
+
 } // namespace blink

third_party/WebKit/Source/core/layout/LayoutTableBoxComponent.h

@@ -10,12 +10,14 @@
 
 namespace blink {
 
+class LayoutTable;
+
 // Common super class for LayoutTableCol, LayoutTableSection and LayoutTableRow.
 class CORE_EXPORT LayoutTableBoxComponent : public LayoutBox {
 public:
     bool backgroundChangedSinceLastPaintInvalidation() const { return m_backgroundChangedSinceLastPaintInvalidation; }
     void clearBackgroundChangedSinceLastPaintInvalidation() { m_backgroundChangedSinceLastPaintInvalidation = false; }
-
+    static bool doCellsHaveDirtyWidth(const LayoutObject& tablePart, const LayoutTable&, const StyleDifference&, const ComputedStyle& oldStyle);
 protected:
     explicit LayoutTableBoxComponent(Element* element)
         : LayoutBox(element)

third_party/WebKit/Source/core/layout/LayoutTableCol.cpp

@@ -45,19 +45,22 @@ LayoutTableCol::LayoutTableCol(Element* element)
 
 void LayoutTableCol::styleDidChange(StyleDifference diff, const ComputedStyle* oldStyle)
 {
+    DCHECK(style()->display() == TABLE_COLUMN || style()->display() == TABLE_COLUMN_GROUP);
+
     LayoutTableBoxComponent::styleDidChange(diff, oldStyle);
 
-    if (LayoutTable* table = this->table()) {
     if (!oldStyle)
         return;
 
+    LayoutTable* table = this->table();
+    if (!table)
+        return;
+
     // TODO(dgrogan): Is the "else" necessary for correctness or just a brittle optimization? The optimization would be:
     // if the first branch is taken then the next one can't be, so don't even check its condition.
     if (!table->selfNeedsLayout() && !table->normalChildNeedsLayout() && oldStyle->border() != style()->border()) {
-            // If border was changed, notify table.
         table->invalidateCollapsedBorders();
-        } else if ((oldStyle->logicalWidth() != style()->logicalWidth()) || (diff.needsFullLayout() && needsLayout() && table->collapseBorders() && oldStyle->border().sizeEquals(style()->border()))) {
-            // TODO(dgrogan): Move second clause above to LayoutTableBoxComponent for re-use.
+    } else if ((oldStyle->logicalWidth() != style()->logicalWidth()) || LayoutTableBoxComponent::doCellsHaveDirtyWidth(*this, *table, diff, *oldStyle)) {
         // TODO(dgrogan): Optimization opportunities:
         // (1) Only mark cells which are affected by this col, not every cell in the table.
         // (2) If only the col width changes and its border width doesn't, do the cells need to be marked as
@@ -69,7 +72,6 @@ void LayoutTableCol::styleDidChange(StyleDifference diff, const ComputedStyle* o
             section->markAllCellsWidthsDirtyAndOrNeedsLayout(LayoutTableSection::MarkDirtyAndNeedsLayout);
         }
     }
-    }
 }
 
 void LayoutTableCol::updateFromElement()

third_party/WebKit/Source/core/layout/LayoutTableRow.cpp

@@ -60,16 +60,22 @@ void LayoutTableRow::styleDidChange(StyleDifference diff, const ComputedStyle* o
     LayoutTableBoxComponent::styleDidChange(diff, oldStyle);
     propagateStyleToAnonymousChildren();
 
-    if (section() && oldStyle && style()->logicalHeight() != oldStyle->logicalHeight())
+    if (!oldStyle)
+        return;
+
+    if (section() && style()->logicalHeight() != oldStyle->logicalHeight())
         section()->rowLogicalHeightChanged(this);
 
-    // If border was changed, notify table.
-    if (parent()) {
+    if (!parent())
+        return;
     LayoutTable* table = this->table();
-        if (table && !table->selfNeedsLayout() && !table->normalChildNeedsLayout() && oldStyle && oldStyle->border() != style()->border())
+    if (!table)
+        return;
+
+    if (!table->selfNeedsLayout() && !table->normalChildNeedsLayout() && oldStyle->border() != style()->border())
         table->invalidateCollapsedBorders();
 
-        if (table && oldStyle && diff.needsFullLayout() && needsLayout() && table->collapseBorders() && oldStyle->border().sizeEquals(style()->border())) {
+    if (LayoutTableBoxComponent::doCellsHaveDirtyWidth(*this, *table, diff, *oldStyle)) {
         // If the border width changes on a row, we need to make sure the cells in the row know to lay out again.
         // This only happens when borders are collapsed, since they end up affecting the border sides of the cell
         // itself.
@@ -88,7 +94,6 @@ void LayoutTableRow::styleDidChange(StyleDifference diff, const ComputedStyle* o
         // TODO(dgrogan): Make LayoutTableSection clear its dirty bit.
         table->setPreferredLogicalWidthsDirty();
     }
-    }
 }
 
 const BorderValue& LayoutTableRow::borderAdjoiningStartCell(const LayoutTableCell* cell) const

third_party/WebKit/Source/core/layout/LayoutTableSection.cpp

@@ -119,17 +119,23 @@ LayoutTableSection::~LayoutTableSection()
 
 void LayoutTableSection::styleDidChange(StyleDifference diff, const ComputedStyle* oldStyle)
 {
+    DCHECK(style()->display() == TABLE_FOOTER_GROUP || style()->display() == TABLE_ROW_GROUP || style()->display() == TABLE_HEADER_GROUP);
+
     LayoutTableBoxComponent::styleDidChange(diff, oldStyle);
     propagateStyleToAnonymousChildren();
 
-    // If border was changed, notify table.
+    if (!oldStyle)
+        return;
+
     LayoutTable* table = this->table();
-    if (table && !table->selfNeedsLayout() && !table->normalChildNeedsLayout() && oldStyle && oldStyle->border() != style()->border())
+    if (!table)
+        return;
+
+    if (!table->selfNeedsLayout() && !table->normalChildNeedsLayout() && oldStyle->border() != style()->border())
         table->invalidateCollapsedBorders();
 
-    if (table && oldStyle && diff.needsFullLayout() && needsLayout() && table->collapseBorders() && oldStyle->border() != style()->border()) {
+    if (LayoutTableBoxComponent::doCellsHaveDirtyWidth(*this, *table, diff, *oldStyle))
         markAllCellsWidthsDirtyAndOrNeedsLayout(MarkDirtyAndNeedsLayout);
-    }
 }
 
 void LayoutTableSection::willBeRemovedFromTree()

third_party/WebKit/Source/core/style/BorderData.h

@@ -126,10 +126,10 @@ public:
 
     bool sizeEquals(const BorderData& o) const
     {
-        return borderLeftWidth() != o.borderLeftWidth()
-            || borderTopWidth() != o.borderTopWidth()
-            || borderRightWidth() != o.borderRightWidth()
-            || borderBottomWidth() != o.borderBottomWidth();
+        return borderLeftWidth() == o.borderLeftWidth()
+            && borderTopWidth() == o.borderTopWidth()
+            && borderRightWidth() == o.borderRightWidth()
+            && borderBottomWidth() == o.borderBottomWidth();
     }
 
     const BorderValue& left() const { return m_left; }