Add minimize button assets for panel windows.

ash/wm/frame_painter.cc

Index: ash/wm/frame_painter.cc
diff --git a/ash/wm/frame_painter.cc b/ash/wm/frame_painter.cc
index d859c12f1aa0e05d6008ab7b33d185ff2797e375..6817a752fd36f9e57ce19a245f2fecc6ab53829a 100644
--- a/ash/wm/frame_painter.cc
+++ b/ash/wm/frame_painter.cc
@@ -510,26 +510,34 @@ void FramePainter::LayoutHeader(views::NonClientFrameView* view,
                     IDR_AURA_WINDOW_MAXIMIZED_CLOSE2_H,
                     IDR_AURA_WINDOW_MAXIMIZED_CLOSE2_P);
     // The chat window cannot be restored but only minimized.
-    // Case: (size_button_behavior_ == SIZE_BUTTON_MINIMIZES). We used to have
-    // a special set of artwork to show this case, but per discussion we
-    // removed this.
-    SetButtonImages(size_button_,
-                    IDR_AURA_WINDOW_MAXIMIZED_RESTORE2,
-                    IDR_AURA_WINDOW_MAXIMIZED_RESTORE2_H,
-                    IDR_AURA_WINDOW_MAXIMIZED_RESTORE2_P);
+    if (size_button_behavior_ == SIZE_BUTTON_MINIMIZES) {
+      SetButtonImages(size_button_,
+                      IDR_AURA_WINDOW_MINIMIZE_SHORT,
+                      IDR_AURA_WINDOW_MINIMIZE_SHORT_H,
+                      IDR_AURA_WINDOW_MINIMIZE_SHORT_P);
+    } else {
+      SetButtonImages(size_button_,
+                      IDR_AURA_WINDOW_MAXIMIZED_RESTORE2,
+                      IDR_AURA_WINDOW_MAXIMIZED_RESTORE2_H,
+                      IDR_AURA_WINDOW_MAXIMIZED_RESTORE2_P);
+    }
   } else if (shorter_layout) {
     SetButtonImages(close_button_,
                     IDR_AURA_WINDOW_MAXIMIZED_CLOSE,
                     IDR_AURA_WINDOW_MAXIMIZED_CLOSE_H,
                     IDR_AURA_WINDOW_MAXIMIZED_CLOSE_P);
     // The chat window cannot be restored but only minimized.
-    // Case: (size_button_behavior_ == SIZE_BUTTON_MINIMIZES). We used to have
-    // a special set of artwork to show this case, but per discussion we
-    // removed this.
-    SetButtonImages(size_button_,
-                    IDR_AURA_WINDOW_MAXIMIZED_RESTORE,
-                    IDR_AURA_WINDOW_MAXIMIZED_RESTORE_H,
-                    IDR_AURA_WINDOW_MAXIMIZED_RESTORE_P);
+    if (size_button_behavior_ == SIZE_BUTTON_MINIMIZES) {
+      SetButtonImages(size_button_,
+                      IDR_AURA_WINDOW_MINIMIZE_SHORT,
+                      IDR_AURA_WINDOW_MINIMIZE_SHORT_H,
+                      IDR_AURA_WINDOW_MINIMIZE_SHORT_P);
+    } else {
+      SetButtonImages(size_button_,
+                      IDR_AURA_WINDOW_MAXIMIZED_RESTORE,
+                      IDR_AURA_WINDOW_MAXIMIZED_RESTORE_H,
+                      IDR_AURA_WINDOW_MAXIMIZED_RESTORE_P);
+    }
   } else {
     SetButtonImages(close_button_,
                     IDR_AURA_WINDOW_CLOSE,