Add a thread-properties API
(Based on proposal at https://sourceware.org/glibc/wiki/ThreadPropertiesAPI)

This includes API to:
 - locate static and dynamic TLS
 - register thread-exit and  dynamic TLS creation/destruction callbacks

Change-Id: Icd9d29a5b2f47495395645e19d3b2c96826f19c8
diff --git a/libc/private/bionic_allocator.h b/libc/private/bionic_allocator.h
index c705ce4..342fd51 100644
--- a/libc/private/bionic_allocator.h
+++ b/libc/private/bionic_allocator.h
@@ -110,6 +110,11 @@
   // Note that this implementation of realloc never shrinks allocation
   void* realloc(void* ptr, size_t size);
   void free(void* ptr);
+
+  // Returns the size of the given allocated heap chunk, if it is valid.
+  // Otherwise, this may return 0 or cause a segfault if the pointer is invalid.
+  size_t get_chunk_size(void* ptr);
+
  private:
   void* alloc_mmap(size_t align, size_t size);
   inline void* alloc_impl(size_t align, size_t size);