Convert CdmAttachedCB into OnceCallback.

Bug: 1007769
Change-Id: I8b864634100fecbb9cfd6ba9a97dd035c1e6da61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1883472
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/master@{#710705}
30 files changed