Update from chromium https://crrev.com/302282

third_party/boringssl/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Config for us and everybody else depending on BoringSSL.
 config("openssl_config") {
   include_dirs = []
   include_dirs += [ "src/include" ]
   if (is_component_build) {
     defines = [
       "BORINGSSL_SHARED_LIBRARY",
     ]
   }
 }
 
 # Config internal to this build file.
 config("openssl_internal_config") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
 }
 
 # The list of BoringSSL files is kept in boringssl.gypi.
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
     [ rebase_path("//third_party/boringssl/boringssl.gypi") ],
     "scope",
     [ "//third_party/boringssl/boringssl.gypi" ])
 
+# Win32's assembly is built by Yasm. The other ports use the platform assembler.
+if (cpu_arch == "x86" && is_win) {
+  import("//third_party/yasm/yasm_assemble.gni")
+  yasm_assemble("boringssl_asm") {
+    sources = gypi_values.boringssl_win_x86_sources
+  }
+}
+
 component("boringssl") {
   sources = gypi_values.boringssl_lib_sources
 
   public_configs = [ ":openssl_config" ]
 
   cflags = []
   defines = [
     "BORINGSSL_IMPLEMENTATION",
     "BORINGSSL_NO_STATIC_INITIALIZER",
   ]
@@ skipping 23 matching lines @@
     } else if (is_win) {
       sources += gypi_values.boringssl_win_x86_64_sources
     } else {
       defines += [ "OPENSSL_NO_ASM" ]
     }
   } else if (cpu_arch == "x86") {
     if (is_mac) {
       sources += gypi_values.boringssl_mac_x86_sources
     } else if (is_linux || is_android) {
       sources += gypi_values.boringssl_linux_x86_sources
+    } else if (is_win) {
+      deps += [ ":boringssl_asm" ]
     } else {
       defines += [ "OPENSSL_NO_ASM" ]
     }
   } else if (cpu_arch == "arm") {
     sources += gypi_values.boringssl_linux_arm_sources
   } else {
     defines += [ "OPENSSL_NO_ASM" ]
   }
 }