Merged a bit of code from Navigation branch to ease further merging (InnerRect is currently not required in the Master branch)

imgui_internal.h

@@ -714,6 +714,7 @@ struct IMGUI_API ImGuiWindow
     ImVector<ImGuiID>       IDStack;                            // ID stack. ID are hashes seeded with the value at the top of the stack
     ImRect                  ClipRect;                           // = DrawList->clip_rect_stack.back(). Scissoring / clipping rectangle. x1, y1, x2, y2.
     ImRect                  WindowRectClipped;                  // = WindowRect just after setup in Begin(). == window->Rect() for root window.
+    ImRect                  InnerRect;
     int                     LastFrameActive;
     float                   ItemWidthDefault;
     ImGuiSimpleColumns      MenuColumns;                        // Simplified columns storage for menu items