[js-code-coverage] Add v8-to-istanbul & source-map npm libs

Add the following packages to third_party/node
- istanbuljs/v8-to-istanbul v7.1.2
- mozilla/source-map v0.7.3

These have been approved by chrome-eng-review:
https://groups.google.com/a/google.com/g/chrome-eng-review/c/l10lJSzM704/m/AjEk9QP0CQAJ

node_modules.tar.gz Before:
Size: 9,713,595 bytes
Files in archive: 9,010

node_modules.tar.gz After:
Size: 9,931,330 bytes (+217,735 bytes)
Files in archive: 9,046 (+36)

Bug: 1211595
Test: ./update_npm_deps and upload resultant node_modules.tar.gz
Change-Id: I5af796d5a04cc1e1df5eadeaa19d5f56b56b43fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2911153
Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: Ben Reich <benreich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#886989}

third_party/node/README.chromium

@@ -50,3 +50,32 @@ readable, standards-based JavaScript.
 
 Local Modifications:
 (none)
+
+Name: V8 to Istanbul Coverage Converter
+Short Name: v8-to-istanbul
+URL: https://www.npmjs.com/package/v8-to-istanbul
+Version: 7.1.2
+License: ISC
+Security Critical: No. Not shipped in Chrome, used for post-processing of coverage reports.
+
+Description:
+V8 To Istanbul converts raw v8 coverage into istanbul compliant coverage report.
+
+Local Modifications:
+(none)
+
+Name: Source map
+Short Name: source-map
+URL: https://www.npmjs.com/package/source-map
+Version: 0.7.3
+License: BSD-3-Clause
+Security Critical: No. Not shipped in Chrome, used to generate source maps for build steps.
+
+Description:
+Source map provides useful functionality to easily generate and consume
+JavaScript source maps, useful in identifying the build transformations that
+occurred between the final generated JavaScript file and the source it
+originated from.
+
+Local Modifications:
+(none)

third_party/node/node_modules.tar.gz.sha1

@@ -1 +1 @@
-b0b96e310b8aa9adc0a36a2dbe12ebf393235f53
+0740a660dfed46eba68b3556368cb40f0ead0daa

third_party/node/npm_exclude.txt

@@ -20,3 +20,8 @@ powered-test/es6-destructuring-assignments.js
 *.map
 typescript/lib/*
 typescript/loc/*
+*.markdown
+*.flow
+lcov.info
+travis-gh-pages
+*/lcov-report/*