exo: Prevent maximize/minimize of shell surface in system modal container.

components/exo/shell_surface.cc

Index: components/exo/shell_surface.cc
diff --git a/components/exo/shell_surface.cc b/components/exo/shell_surface.cc
index c820038ac88d2363341be014881bbb19c4daffa6..72f11c53c45055919cd6cbcda9f83703788b3c8d 100644
--- a/components/exo/shell_surface.cc
+++ b/components/exo/shell_surface.cc
@@ -652,11 +652,13 @@ bool ShellSurface::CanResize() const {
 }
 
 bool ShellSurface::CanMaximize() const {
-  return true;
+  // Shell surfaces in system modal container cannot be maximized.
+  return container_ != ash::kShellWindowId_SystemModalContainer;
 }
 
 bool ShellSurface::CanMinimize() const {
-  return true;
+  // Shell surfaces in system modal container cannot be minimized.
+  return container_ != ash::kShellWindowId_SystemModalContainer;
 }
 
 base::string16 ShellSurface::GetWindowTitle() const {