[css-grid] Implement fit-content track size

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

Index: third_party/WebKit/Source/core/style/GridTrackSize.h
diff --git a/third_party/WebKit/Source/core/style/GridTrackSize.h b/third_party/WebKit/Source/core/style/GridTrackSize.h
index 9cd614951b61226eb012bae0ef1d4122ff171239..5005aed0e7a8d64b1898cb762a054263930537af 100644
--- a/third_party/WebKit/Source/core/style/GridTrackSize.h
+++ b/third_party/WebKit/Source/core/style/GridTrackSize.h
@@ -38,19 +38,25 @@ namespace blink {
 
 enum GridTrackSizeType {
     LengthTrackSizing,
-    MinMaxTrackSizing
+    MinMaxTrackSizing,
+    FitContentTrackSizing
 };
 
+// This class represents a <track-size> from the spec. Althought there are 3 different types of
+// <track-size> there is always an equivalent minmax() representation that could represent any of
+// them. The only special case is fit-content(argument) which is similar to minmax(auto, max-content)
+// except that the track size is clamped at argument if it is greater than the auto minimum. At the
+// GridTrackSize level we don't need to worry about clamping so we treat that case exactly as
+// minmax(auto, max-content) althought we store the argument for later use in m_maxTrackBreadth.
 class GridTrackSize {
     DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 public:
-    GridTrackSize(const GridLength& length)
-        : m_type(LengthTrackSizing)
-        , m_minTrackBreadth(length)
+    GridTrackSize(const GridLength& length, GridTrackSizeType trackSizeType = LengthTrackSizing)
+        : m_type(trackSizeType)
+        , m_minTrackBreadth(trackSizeType == FitContentTrackSizing ? Length(Auto) : length)
         , m_maxTrackBreadth(length)
-        , m_minTrackBreadthIsMaxContent(false)
-        , m_maxTrackBreadthIsMaxContent(false)
     {
+        DCHECK(trackSizeType == LengthTrackSizing || trackSizeType == FitContentTrackSizing);
         cacheMinMaxTrackBreadthTypes();
     }
 
@@ -58,27 +64,24 @@ public:
         : m_type(MinMaxTrackSizing)
         , m_minTrackBreadth(minTrackBreadth)
         , m_maxTrackBreadth(maxTrackBreadth)
-        , m_minTrackBreadthIsMaxContent(false)
-        , m_maxTrackBreadthIsMaxContent(false)
     {
         cacheMinMaxTrackBreadthTypes();
     }
 
-    const GridLength& length() const
+    GridLength length() const
     {
-        ASSERT(m_type == LengthTrackSizing);
-        ASSERT(m_minTrackBreadth == m_maxTrackBreadth);
-        const GridLength& minTrackBreadth = m_minTrackBreadth;
-        return minTrackBreadth;
+        DCHECK(m_type == LengthTrackSizing || m_type == FitContentTrackSizing);
+        DCHECK(m_minTrackBreadth == m_maxTrackBreadth || m_type == FitContentTrackSizing);
+        return m_maxTrackBreadth;
     }
 
-    const GridLength& minTrackBreadth() const { return m_minTrackBreadth; }
-
-    const GridLength& maxTrackBreadth() const { return m_maxTrackBreadth; }
+    GridLength minTrackBreadth() const { return m_minTrackBreadth; }
+    GridLength maxTrackBreadth() const { return isFitContent() ? GridLength(Length(MaxContent)) : m_maxTrackBreadth; }
 
     GridTrackSizeType type() const { return m_type; }
 
     bool isContentSized() const { return m_minTrackBreadth.isContentSized() || m_maxTrackBreadth.isContentSized(); }
+    bool isFitContent() const { return m_type == FitContentTrackSizing; }
 
     bool operator==(const GridTrackSize& other) const
     {