Ignores screenshot taking invocations if it's too close to the previous one.

ash/accelerators/accelerator_controller_unittest.cc

Index: ash/accelerators/accelerator_controller_unittest.cc
diff --git a/ash/accelerators/accelerator_controller_unittest.cc b/ash/accelerators/accelerator_controller_unittest.cc
index fde725997b715c70115ac39ae1846c9e4a928ef8..d2af94ce8e644a36534569bc40d1099ec54beec6 100644
--- a/ash/accelerators/accelerator_controller_unittest.cc
+++ b/ash/accelerators/accelerator_controller_unittest.cc
@@ -81,6 +81,10 @@ class DummyScreenshotDelegate : public ScreenshotDelegate {
     ++handle_take_partial_screenshot_count_;
   }
 
+  virtual bool CanTakeScreenshot() OVERRIDE {
+    return true;
+  }
+
   int handle_take_screenshot_count() const {
     return handle_take_screenshot_count_;
   }