feat: make it possible to run install.js script with puppeteer-core (#5325)

Co-authored-by: Mathias Bynens <mathias@qiwi.be>

docs/api.md

@@ -371,6 +371,7 @@ In most cases, you'll be fine using the `puppeteer` package.
 However, you should use `puppeteer-core` if:
 - you're building another end-user product or library atop of DevTools protocol. For example, one might build a PDF generator using `puppeteer-core` and write a custom `install.js` script that downloads [`headless_shell`](https://chromium.googlesource.com/chromium/src/+/lkgr/headless/README.md) instead of Chromium to save disk space.
 - you're bundling Puppeteer to use in Chrome Extension / browser with the DevTools protocol where downloading an additional Chromium binary is unnecessary.
+- you're building a set of tools where `puppeteer-core` is one of the ingredients and you want to postpone `install.js` script execution until Chromium is about to be used.
 
 When using `puppeteer-core`, remember to change the *include* line:
 

install.js

@@ -14,10 +14,14 @@
  * limitations under the License.
  */
 
-// puppeteer-core should not install anything.
-if (require('./package.json').name === 'puppeteer-core')
-  return;
-
+/**
+ * This file is part of public API.
+ *
+ * By default, the `puppeteer` package runs this script during the installation
+ * process unless one of the env flags is provided.
+ * `puppeteer-core` package doesn't include this step at all. However, it's
+ * still possible to install Chromium using this script when necessary.
+ */
 if (process.env.PUPPETEER_SKIP_CHROMIUM_DOWNLOAD) {
   logPolitely('**INFO** Skipping Chromium download. "PUPPETEER_SKIP_CHROMIUM_DOWNLOAD" environment variable was found.');
   return;

utils/prepare_puppeteer_core.js

@@ -22,4 +22,5 @@ const packagePath = path.join(__dirname, '..', 'package.json');
 const json = require(packagePath);
 
 json.name = 'puppeteer-core';
+delete json.scripts.install;
 fs.writeFileSync(packagePath, JSON.stringify(json, null, '  '));