Split upb::Arena/upb::Allocator from upb::Environment. (#58)

* Split upb::Arena/upb::Allocator from upb::Environment.

This will allow arenas and allocators to be used
independently of environments, which will be important
for an upcoming change (a message representation).
Overall this design feels cleaner that the previous
Environment/SeededAllocator design.

As part of this change, moved all allocations in upb
to use a global allocator instead of hard-coding
malloc/free.  This will allow injecting OOM faults
for more robust testing.

One place that doesn't use the global allocator is
the tracked ref code.  Instead of its previous approach
of CHECK_OOM() after every malloc() or table insert, it
simply uses an allocator that does this automatically.

I moved Allocator/Arena/Environment into upb.h.
This seems principled since these are the only types
in upb whose size is directly exposed to users, since
they form the basis of memory allocation strategy.

* Cleaned up some header includes and fixed more malloc -> upb_gmalloc().

* Changes from PR review.

* Don't use UINTPTR_MAX or UINT64_MAX.

* Punt on adding line/file for now.

* We actually can't store (uint64_t)-1, update comment and test.

1 files changed, 2 insertions, 1 deletions

diff --git a/upb/pb/glue.h b/upb/pb/glue.h
index 014562b..8f570bc 100644
--- a/upb/pb/glue.h
+++ b/upb/pb/glue.h
@@ -31,7 +31,8 @@ extern "C" {
 #endif
 
 /* Loads a binary descriptor and returns a NULL-terminated array of unfrozen
- * filedefs.  The caller owns the returned array. */
+ * filedefs.  The caller owns the returned array, which must be freed with
+ * upb_gfree(). */
 upb_filedef **upb_loaddescriptor(const char *buf, size_t n, const void *owner,
                                  upb_status *status);