Cache animated image's frame index

Cache animated image's frame index

There is no reason to multiple decoding for same-image's same-frame loading.
It just increase our memory useage and CPU usage.

This patch cache animated image's frame index so
we can re-use already decoded frame informations.

+

For more, Due to the animated image decoding can hold big amount of observers
in one frame, we need to reduce runtime of NotifyObservers API.
This patch also reduce NotifyObservers time complexity from O(N^2) to O(N).
Note : We can't add additional observer due to the mQueueLoadFlag flag is true.

Change-Id: I829704c638ce7b6a5feca13cc1bcf75b4bd9e35e
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>