Make VDA::Config's converting constructor explicit

This CL makes VDA::Config's converting constructor
explicit to avoid implicit conversions.

BUG=None
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2901753002
Cr-Original-Commit-Position: refs/heads/master@{#475073}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f8d975ed29b6f665d66b1e57736f788a1bcfe287
2 files changed