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..62672d02532e9b4e4700f70f1c1a66778845c07b 100644
--- a/ui/views/layout/box_layout.h
+++ b/ui/views/layout/box_layout.h
@@ -105,6 +105,31 @@ 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 aware of the per-view margins.
+  // 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. 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.
+  struct ViewWrapper {
+    ViewWrapper();
+    ViewWrapper(View* view);
+    ViewWrapper(const ViewWrapper& wrapper) = delete;
+    ~ViewWrapper();
+    int GetHeightForWidth(int width) const;
+    gfx::Size GetPreferredSize() const;
+    void SetBoundsRect(const gfx::Rect& bounds);
+    View* view() const { return view_; }
+    bool visible() const;
+
+   private:
+    View* view_;
+    gfx::Insets margins_;
+  };
+
+  using FlexMap = std::map<const View*, int>;
+
   // Returns the flex for the specified |view|.
   int GetFlexForView(const View* view) const;
 
@@ -126,10 +151,10 @@ 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 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,
@@ -156,7 +181,7 @@ 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_;