[Win/boringSSL] Add nasm as part of required dependencies.

In order to fix the roll https://webrtc-review.googlesource.com/c/src/+/110080,
this CL updates WebRTC DEPS to be on a par with Chromium's CL:
"Add nasm support to Chromium, use it for boringssl."
7d284aff8c

Bug: chromium:766721
Change-Id: I048116f6ec49876a1b878097efff631db8cafe68
Reviewed-on: https://webrtc-review.googlesource.com/c/110340
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Commit-Queue: Yves Gerey <yvesg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25573}

DEPS

@@ -169,6 +169,13 @@ deps = {
     'url': Var('chromium_git') + '/external/mockito/mockito.git' + '@' + '04a2a289a4222f80ad20717c25144981210d2eac',
     'condition': 'checkout_android',
   },
+
+  # Used by boringssl.
+  'src/third_party/nasm': {
+      'url': Var('chromium_git') + '/chromium/deps/nasm.git' + '@' +
+      '20920a85609b0608d4c9c80b525196d07183b289'
+  },
+
   'src/third_party/openh264/src':
     Var('chromium_git') + '/external/github.com/cisco/openh264' + '@' + '3b51f16a4a41df729f8d647f03e48c5f272911ff',
   'src/third_party/r8': {