Poison hashtable buffers.

MozReview-Commit-ID: 8uLGtFv6X4P

components/hashglobe/src/table.rs

@@ -777,13 +777,16 @@ impl<K, V> RawTable<K, V> {
 
 
         // FORK NOTE: Uses alloc shim instead of Heap.alloc
-        let buffer = alloc(size, alignment);
+        let buffer: *mut u8 = alloc(size, alignment);
 
         if buffer.is_null() {
 
             return Err(FailedAllocationError { reason: "out of memory when allocating RawTable" });
         }
 
+        // FORK NOTE: poison the entire buffer rather than leaving it uninitialized.
+        ptr::write_bytes(buffer, 0xe7, size);
+
         let hashes = buffer.offset(hash_offset as isize) as *mut HashUint;
 
         Ok(RawTable {