Add missing events_devices dependency for chrome_brower_chromeos

Missing dependency introduced in r314400 ("Make PointerDeviceObserver
work under Ozone").

TEST=link_freon component build
BUG=450899

Review URL: https://codereview.chromium.org/896723007

Cr-Commit-Position: refs/heads/master@{#314434}

chrome/chrome_browser_chromeos.gypi

@@ -1141,6 +1141,7 @@
         '../third_party/zlib/zlib.gyp:zlib',
         '../ui/base/ui_base.gyp:ui_base',
         '../ui/display/display.gyp:display',
+        '../ui/events/devices/events_devices.gyp:events_devices',
         '../ui/events/events.gyp:dom4_keycode_converter',
         '../ui/events/platform/events_platform.gyp:events_platform',
         '../ui/chromeos/ui_chromeos.gyp:ui_chromeos_resources',