DEPS: Update leveldatabase from 1.18 to 1.20.

third_party/leveldatabase/port/port_chromium.h

Index: third_party/leveldatabase/port/port_chromium.h
diff --git a/third_party/leveldatabase/port/port_chromium.h b/third_party/leveldatabase/port/port_chromium.h
index 557945318f6493dedab9f5b4749f8b1ed9cfc6cf..3dc2d986c892da990e8b113b24f9ed5c00393803 100644
--- a/third_party/leveldatabase/port/port_chromium.h
+++ b/third_party/leveldatabase/port/port_chromium.h
@@ -115,7 +115,10 @@ inline bool GetHeapProfile(void (*func)(void*, const char*, int), void* arg) {
   return false;
 }
 
-}
-}
+// Implemented in leveldb's src/port/port_posix_sse.cc.
+uint32_t AcceleratedCRC32C(uint32_t crc, const char* buf, size_t size);
+
+}  // namespace port
+}  // namespace leveldb
 
 #endif  // STORAGE_LEVELDB_PORT_PORT_CHROMIUM_H_