Reland "Integrate SIMD optimisations for zlib"

third_party/zlib/README.chromium

Index: third_party/zlib/README.chromium
diff --git a/third_party/zlib/README.chromium b/third_party/zlib/README.chromium
index c9e06bae394c4334af5ac0874a6f2ebd467271e4..b90bcff42fb7d37bb8bad52239901523a7e1775a 100644
--- a/third_party/zlib/README.chromium
+++ b/third_party/zlib/README.chromium
@@ -19,3 +19,19 @@ The 'google.patch' file represents our changes from the original zlib-1.2.5.
 
 A more significant change to support mixed-source data compression. See
 crbug.com/139744 and mixed-source.patch.
+
+Integrated Intel SIMD optimisations from: https://github.com/jtkukunas/zlib/
+and modified to accomodate the older version and existing changes in tree.
+
+This introduces new files: simd_stub.c, crc_folding.c, fill_window_sse.c and
+x86.[ch]. All but the latter are built into a static library to allow the
+compiler to use the desired instructions only when valid. The latter version is
+only built on x86 (32-bit and 64-bit) systems with it's functionality stubbed
+on the others.
+
+Other changes to accomodate:
+- fill_window() implementation calls into _sse() variant when supported and the
+  original implementation renamed to _c()
+- read_buf was moved from local to ZLIB_INTERNAL for fill_window_sse.c to use
+- INSERT_STRING macro was made a function, insert_string() and an implementation using CRC instruction added
+- some crc funcionality moved into crc32.c