mash: Move ash_switches.* to ash/common; cleanup DEPS.

tools/git/move_source_file.py ash/ash_switches* ash/common/
Fix include in ash/virtual_keyboard_controller_unittest.cc.
Remove explicit ash_switches.h entry from ash/common/DEPS.

BUG=619636
TEST=Compiles, no changes.
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Review-Url: https://codereview.chromium.org/2074213002
Cr-Commit-Position: refs/heads/master@{#400485}
diff --git a/ash/test/ash_test_helper.cc b/ash/test/ash_test_helper.cc
index 23eb96fc..d6a90f0 100644
--- a/ash/test/ash_test_helper.cc
+++ b/ash/test/ash_test_helper.cc
@@ -5,7 +5,7 @@
 #include "ash/test/ash_test_helper.h"
 
 #include "ash/accelerators/accelerator_controller.h"
-#include "ash/ash_switches.h"
+#include "ash/common/ash_switches.h"
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/display/display_info.h"
 #include "ash/shell.h"