accelerators: Disable screenshot accelerators on login screen.

Test: Manually tested on Dut.
Fixed: 1146655
Change-Id: If922581c6987815dacf4277359dcf2ff98a4bd31
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532309
Commit-Queue: Judy Wang <shidi@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826982}

ash/accelerators/accelerator_table.cc

@@ -173,9 +173,6 @@ const AcceleratorAction kActionsAllowedAtLoginOrLockScreen[] = {
     START_AMBIENT_MODE,
     SWITCH_TO_LAST_USED_IME,
     SWITCH_TO_NEXT_IME,
-    TAKE_PARTIAL_SCREENSHOT,
-    TAKE_SCREENSHOT,
-    TAKE_WINDOW_SCREENSHOT,
     TOGGLE_CAPS_LOCK,
     TOGGLE_DICTATION,
     TOGGLE_DOCKED_MAGNIFIER,
@@ -199,7 +196,11 @@ const size_t kActionsAllowedAtLoginOrLockScreenLength =
     base::size(kActionsAllowedAtLoginOrLockScreen);
 
 const AcceleratorAction kActionsAllowedAtLockScreen[] = {
-    EXIT, SUSPEND,
+    EXIT,
+    SUSPEND,
+    TAKE_PARTIAL_SCREENSHOT,
+    TAKE_SCREENSHOT,
+    TAKE_WINDOW_SCREENSHOT,
 };
 
 const size_t kActionsAllowedAtLockScreenLength =