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 63323c44156d76c381d4de6c92596693be7d8cea..53fde45c616be093a537672034fe8a30532a8911 100644
--- a/components/exo/shell_surface.cc
+++ b/components/exo/shell_surface.cc
@@ -651,11 +651,13 @@ 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 {