BoxLayout now suports per-view margins.

ui/views/layout/box_layout.h

Index: ui/views/layout/box_layout.h
diff --git a/ui/views/layout/box_layout.h b/ui/views/layout/box_layout.h
index 9a87984d51f77cec0caa488860fa6dc1986f9e28..0b054fa879da4a732b1e1b66239883168bf69f33 100644
--- a/ui/views/layout/box_layout.h
+++ b/ui/views/layout/box_layout.h
@@ -58,11 +58,57 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
   // Use |inside_border_horizontal_spacing| and
   // |inside_border_vertical_spacing| to add additional space between the child
   // view area and the host view border. |between_child_spacing| controls the
-  // space in between child views.
+  // space in between child views. Use view->SetProperty(kMarginsKey,
+  //   new gfx::Insets(xxx)) to add additional margins on a per-view basis. The
+  // |collapse_margins_spacing| parameter controls whether or not spacing
+  // adjacent to view margins are collapsed base on the max of the two values.
+  //
+  // Given the following views where V = view bounds, M = Margins property,
+  // B = between child spacing, S = inside border spacing and
+  // <space> = added margins for alignment
+  //
+  // MMMMM  MMVVVVMM  MMMM
+  // VVVVM            MMMM
+  // VVVVM            MMMM
+  // VVVVM            VVVV
+  // MMMMM
+  //
+  // With collapse_margins_spacing = false, orientation = kHorizontal,
+  // inside_border_spacing_horizontal = 2, inside_border_spacing_vertical = 2
+  // and between_child_spacing = 1:
+  //
+  // -----------------------
+  // SSSSSSSSSSSSSSSSSSSSSSS
+  // SSSSSSSSSSSSSSSSSSSSSSS
+  // SS    MBMM    MMBMMMMSS
+  // SS    MBMM    MMBMMMMSS
+  // SSMMMMMBMM    MMBMMMMSS
+  // SSVVVVMBMMVVVVMMBVVVVSS
+  // SSVVVVMBMMVVVVMMBVVVVSS
+  // SSVVVVMBMMVVVVMMBVVVVSS
+  // SSMMMMMBMMVVVVMMBVVVVSS
+  // SSSSSSSSSSSSSSSSSSSSSSS
+  // SSSSSSSSSSSSSSSSSSSSSSS
+  // -----------------------
+  //
+  // Same as above except, collapse_margins_spacing = true.
+  //
+  // --------------------
+  // SS          MMMMMMSS
+  // SS          MMMMMMSS
+  // SSMMMMMM    MMMMMMSS
+  // SSVVVVMMVVVVMMVVVVSS
+  // SSVVVVMMVVVVMMVVVVSS
+  // SSVVVVMMVVVVMMVVVVSS
+  // SSSSSSSSSSSSSSSSSSSS
+  // SSSSSSSSSSSSSSSSSSSS
+  // --------------------
+  //
   BoxLayout(Orientation orientation,
             int inside_border_horizontal_spacing,
             int inside_border_vertical_spacing,
-            int between_child_spacing);
+            int between_child_spacing,
+            bool collapse_margins_spacing = false);
   ~BoxLayout() override;
 
   void set_main_axis_alignment(MainAxisAlignment main_axis_alignment) {
@@ -105,6 +151,43 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
   int GetPreferredHeightForWidth(const View* host, int width) const override;
 
  private:
+  // This struct is used internally to "wrap" a child view in order to obviate
+  // the need for the main layout logic to be fully aware of the per-view
+  // margins when |collapse_margin_spacing_| is false. Since each view is a
+  // rectangle of a certain size, this wrapper, coupled with any margins set
+  // will increase the apparent size of the view along the main axis. All
+  // necessary view size/position methods required for the layout logic add or
+  // subtract the margins where appropriate to ensure the actual visible size of
+  // the view doesn't include the margins. For the cross axis, the margins are
+  // NOT included in the size/position calculations. BoxLayout will adjust the
+  // bounding rectangle of the space used for layout using the maximum margin
+  // for all views along the appropriate edge.
+  // When |collapse_margin_spacing_| is true, this wrapper provides quick access
+  // to the view's margins for use by the layout to collapse adjacent spacing
+  // to the largest of the several values.
+  class ViewWrapper {
+   public:
+    ViewWrapper();
+    ViewWrapper(const BoxLayout* layout, View* view);
+    ~ViewWrapper();
+    int GetHeightForWidth(int width) const;
+    const gfx::Insets& margins() const { return margins_; }
+    gfx::Size GetPreferredSize() const;
+    void SetBoundsRect(const gfx::Rect& bounds);
+    View* view() const { return view_; }
+    bool visible() const;
+
+   private:
+    View* view_;
+    const BoxLayout* layout_;
+    const Orientation orientation_;
+    gfx::Insets margins_;
+
+    DISALLOW_COPY_AND_ASSIGN(ViewWrapper);
+  };
+
+  using FlexMap = std::map<const View*, int>;
+
   // Returns the flex for the specified |view|.
   int GetFlexForView(const View* view) const;
 
@@ -126,10 +209,36 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
 
   // Returns the main axis size for the given view. |child_area_width| is needed
   // to calculate the height of the view when the orientation is vertical.
-  int MainAxisSizeForView(const View* view, int child_area_width) const;
+  int MainAxisSizeForView(const ViewWrapper& view, int child_area_width) const;
+
+  // Returns the main axis margin spacing between the two views which is the max
+  // of the right margin from the |left| view, the left margin of the |right|
+  // view and |between_child_spacing_|.
+  int MainAxisMarginBetweenViews(const ViewWrapper& left,
+                                 const ViewWrapper& right) const;
+
+  // Return the outer margin along the main axis as insets.
+  gfx::Insets MainAxisOuterMargin() const;
+
+  // Return the maximum margin along the cross axis from all views as insets.
+  gfx::Insets CrossAxisMaxViewMargin() const;
+
+  // Return the outer margin along the cross axis as insets.
+  gfx::Insets CrossAxisOuterMargin() const;
+
+  // Adjusts the main axis for |rect| by collapsing the left or top margin of
+  // the first view with corresponding side of |inside_border_insets_| and the
+  // right or bottom margin of the last view with the corresponding side of
+  // |inside_border_insets_|.
+  void AdjustMainAxisForMargin(gfx::Rect* rect) const;
+
+  // Adjust the cross axis of |rect| by collapsing the max of the cross axis
+  // margins of all children and the corresponding side of
+  // |inside_border_insets_|
+  void AdjustCrossAxisForMargin(gfx::Rect* rect) const;
 
   // Returns the cross axis size for the given view.
-  int CrossAxisSizeForView(const View* view) const;
+  int CrossAxisSizeForView(const ViewWrapper& view) const;
 
   // The preferred size for the dialog given the width of the child area.
   gfx::Size GetPreferredSizeForChildWidth(const View* host,
@@ -139,6 +248,16 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
   // child views.
   gfx::Size NonChildSize(const View* host) const;
 
+  // The next visible view at > index. If no other views are visible, return
+  // nullptr.
+  View* NextVisibleView(int index) const;
+
+  // Return the first visible view in the host or nullptr if none are visible.
+  View* FirstVisibleView() const;
+
+  // Return the last visible view in the host or nullptr if none are visible.
+  View* LastVisibleView() const;
+
   const Orientation orientation_;
 
   // Spacing between child views and host view border.
@@ -156,7 +275,7 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
   CrossAxisAlignment cross_axis_alignment_;
 
   // A map of views to their flex weights.
-  std::map<const View*, int> flex_map_;
+  FlexMap flex_map_;
 
   // The flex weight for views if none is set. Defaults to 0.
   int default_flex_;
@@ -164,6 +283,9 @@ class VIEWS_EXPORT BoxLayout : public LayoutManager {
   // The minimum cross axis size for the layout.
   int minimum_cross_axis_size_;
 
+  // Adjacent view margins and spacing should be collapsed.
+  const bool collapse_margins_spacing_;
+
   // The view that this BoxLayout is managing the layout for.
   views::View* host_;