class ArenaBase

|ArenaBase| is the base class of all of the |Arena| classes. It is independent

of the initial buffer size. All the implementation is done here. The |Arena|

specializations only exist to define the initial buffer size.

The arena owns all the data which are allocated. That means that the

allocated data can be used by pure views. The allocated data are freed when

the arena is freed.

Users cannot directly call an arena's methods. Instead, they must do so via

|ObjectView|, |StringView| and |VectorView| classes, as well as generated

wire domain objects such as tables and unions. The allocation is first made

within the initial buffer. When the initial buffer is full (or, at least, the

next allocation doesn't fit in the remaining space), the arena allocates

extra buffers on the heap. If one allocation is bigger than the capacity of a

standard extra buffer, a tailored buffer is allocated which only contains the

allocation.

Allocations are put one after the other in the buffers. When a buffer can't

fit the next allocation, the remaining space is lost and another buffer is

allocated on the heap. Each allocation respects |FIDL_ALIGNMENT|. For

allocations which don't need a destructor, we only allocate the requested

size within the buffer. For allocations with a non trivial destructor, we

also allocate some space for a |struct Destructor| which is stored before the

requested data.

The constructor and destructor of |ArenaBase| are private to disallow direct

instantiation.