external/boringssl: Sync to 8ca0b41.

This includes the following changes:

https://boringssl.googlesource.com/boringssl/+log/9d908ba519f2cfe5e21561bdee3e224b94d14a89..8ca0b4127da11d766067ea6ec4122017ba0edb0e

Change-Id: I732653bc8fcba70707c615f8731ca75397a08736
diff --git a/src/include/openssl/buf.h b/src/include/openssl/buf.h
index f4e315c..8ae856b 100644
--- a/src/include/openssl/buf.h
+++ b/src/include/openssl/buf.h
@@ -80,6 +80,10 @@
 /* BUF_MEM_free frees |buf->data| if needed and then frees |buf| itself. */
 OPENSSL_EXPORT void BUF_MEM_free(BUF_MEM *buf);
 
+/* BUF_MEM_reserve ensures |buf| has capacity |cap| and allocates memory if
+ * needed. It returns one on success and zero on error. */
+OPENSSL_EXPORT int BUF_MEM_reserve(BUF_MEM *buf, size_t cap);
+
 /* BUF_MEM_grow ensures that |buf| has length |len| and allocates memory if
  * needed. If the length of |buf| increased, the new bytes are filled with
  * zeros. It returns the length of |buf|, or zero if there's an error. */