Store IdTargetObserver::m_registry as a reference

Store IdTargetObserver::m_registry as a reference

Store IdTargetObserver::m_registry as a reference instead of a pointer.
This makes the code look safer and gets rid of an unnecessary null check.

Also make IdTargetObserverRegistry non copyable to protect against bad
assignments to references.

R=adamk@chromium.org, adamk, rwlbuis

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168419

[adamk, 2014-03-04 05:00:32]

lgtm

[commit-bot: I haz the power, 2014-03-04 05:00:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/183463004/1

[Inactive, 2014-03-05 02:47:41]

Committed patchset #2 manually as r168419 (presubmit successful).