Handle nil return from ColorSyncDeviceCopyDeviceInfo.

ColorSyncDeviceCopyDeviceInfo sometimes returns nil. The GPU test framework
should gracefully handle this failure.

Bug: 888035
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I6374f2ef01e6272a7220a030e1e0ff5ecdaa80b9
Reviewed-on: https://chromium-review.googlesource.com/1238780Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593596}

content/test/gpu/gpu_tests/color_profile_manager_mac.py

@@ -80,6 +80,8 @@ def GetDisplaysToProfileURLMap():
     device_info = ColorSyncDeviceCopyDeviceInfo(
         kColorSyncDisplayDeviceClass,
         CGDisplayCreateUUIDFromDisplayID(display_id))
+    if not device_info:
+      raise Exception('KVM connection on bot is broken, please file a bug')
     device_id = device_info['DeviceID']
     custom_profile_url = None
     if 'CustomProfiles' in device_info and '1' in device_info['CustomProfiles']: