Adds a new method IGBP::allowAllocation, which controls whether
dequeueBuffer is permitted to allocate a new buffer. If allocation is
disallowed, dequeueBuffer will block or return an error as it
normally would (as controlled by *ControlledByApp).
If there are free buffers, but they are not of the correct dimensions,
format, or usage, they may be freed if a more suitable buffer is not
found first.
Bug: 19801715
Change-Id: I0d604958b78b2fd775c2547690301423f9a52165
9de7293b0a