Allow the user to cancel the capture region action, and show its active status in the tray.

ash/shell/shell_delegate_impl.cc

Index: ash/shell/shell_delegate_impl.cc
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index 280116865d69f098dc6eca576b815cacebe87b3d..55e2e1af9f05f257c665ec9918707ab545ea6e49 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -98,7 +98,8 @@ class PaletteDelegateImpl : public PaletteDelegate {
   bool ShouldAutoOpenPalette() override { return false; }
   bool ShouldShowPalette() override { return false; }
   void TakeScreenshot() override {}
-  void TakePartialScreenshot() override {}
+  void TakePartialScreenshot(const base::Closure& done) override {}

[oshima, 2016/09/02 13:55:19]

nit: you may want to just run the callback for consistent behavior.

[jdufault, 2016/09/02 19:46:31]

Done.

+  void CancelPartialScreenshot() override {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PaletteDelegateImpl);