Re-land 71230....

views/controls/single_split_view.h

Index: views/controls/single_split_view.h
===================================================================
--- views/controls/single_split_view.h	(revision 71256)
+++ views/controls/single_split_view.h	(working copy)
@@ -6,12 +6,16 @@
 #define VIEWS_CONTROLS_SINGLE_SPLIT_VIEW_H_
 #pragma once
 
+#include "base/gtest_prod_util.h"
 #include "views/view.h"
 
 namespace views {
 
-// SingleSplitView lays out two views horizontally. A splitter exists between
-// the two views that the user can drag around to resize the views.
+// SingleSplitView lays out two views next to each other, either horizontally
+// or vertically. A splitter exists between the two views that the user can
+// drag around to resize the views.
+// Observer's SplitHandleMoved notification helps to monitor user initiated
+// layout changes.
 class SingleSplitView : public views::View {
  public:
   enum Orientation {
@@ -19,8 +23,22 @@
     VERTICAL_SPLIT
   };
 
-  SingleSplitView(View* leading, View* trailing, Orientation orientation);
+  class Observer {
+   public:
+    // Invoked when split handle is moved by the user. |source|'s divider_offset
+    // is already set to the new value, but Layout has not happened yet.
+    // Returns false if the layout has been handled by the observer, returns
+    // true if |source| should do it by itself.
+    virtual bool SplitHandleMoved(SingleSplitView* source) = 0;
+   protected:
+    virtual ~Observer() {}
+  };
 
+  SingleSplitView(View* leading,
+                  View* trailing,
+                  Orientation orientation,
+                  Observer* observer);
+
   virtual void DidChangeBounds(const gfx::Rect& previous,
                                const gfx::Rect& current);
 
@@ -36,10 +54,14 @@
   virtual gfx::NativeCursor GetCursorForPoint(Event::EventType event_type,
                                               const gfx::Point& p);
 
+  Orientation orientation() const {
+    return is_horizontal_ ? HORIZONTAL_SPLIT : VERTICAL_SPLIT;
+  }
+
   void set_divider_offset(int divider_offset) {
     divider_offset_ = divider_offset;
   }
-  int divider_offset() { return divider_offset_; }
+  int divider_offset() const { return divider_offset_; }
 
   // Sets whether the leading component is resized when the split views size
   // changes. The default is true. A value of false results in the trailing
@@ -48,21 +70,42 @@
     resize_leading_on_bounds_change_ = resize;
   }
 
+  // Calculates ideal leading and trailing view bounds according to the given
+  // split view |bounds|, current divider offset and children visiblity.
+  // Does not change children view bounds.
+  void CalculateChildrenBounds(const gfx::Rect& bounds,
+                               gfx::Rect* leading_bounds,
+                               gfx::Rect* trailing_bounds) const;
+
  protected:
   virtual bool OnMousePressed(const MouseEvent& event);
   virtual bool OnMouseDragged(const MouseEvent& event);
   virtual void OnMouseReleased(const MouseEvent& event, bool canceled);
 
  private:
+  // This test calls OnMouse* functions.
+  FRIEND_TEST_ALL_PREFIXES(SingleSplitViewTest, MouseDrag);
+
   // Returns true if |x| or |y| is over the divider.
   bool IsPointInDivider(const gfx::Point& p);
 
+  // Calculates the new |divider_offset| based on the changes of split view
+  // bounds.
+  int CalculateDividerOffset(
+      int divider_offset,
+      const gfx::Rect& previous_bounds,
+      const gfx::Rect& new_bounds) const;
+
+  // Returns divider offset within primary axis size range for given split
+  // view |bounds|.
+  int NormalizeDividerOffset(int divider_offset, const gfx::Rect& bounds) const;
+
   // Returns width in case of horizontal split and height otherwise.
-  int GetPrimaryAxisSize() {
+  int GetPrimaryAxisSize() const {
     return GetPrimaryAxisSize(width(), height());
   }
 
-  int GetPrimaryAxisSize(int h, int v) {
+  int GetPrimaryAxisSize(int h, int v) const {
     return is_horizontal_ ? h : v;
   }
 
@@ -84,6 +127,9 @@
 
   bool resize_leading_on_bounds_change_;
 
+  // Observer to notify about user initiated handle movements. Not own by us.
+  Observer* observer_;
+
   DISALLOW_COPY_AND_ASSIGN(SingleSplitView);
 };