Add a manifest property declaring USB printers supported by an app.

chrome/common/extensions/docs/templates/articles/manifest/usb_printers.html

Index: chrome/common/extensions/docs/templates/articles/manifest/usb_printers.html
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+<h1>Manifest - USB Printers</h1>
+
+<p>
+The <code>usbPrinters</code> manifest property declares which USB printers are supported by an app using the $(ref:printerProvider) API.
+</p>
+
+<h2 id="manifest">Sample manifest.json</h2>
+<pre data-filename="manifest.json">
+{
+  "name": "My printer {{platform}}",
+  "usb_printers": {
+    "filters": [
+      // This app can print to the Nexus One and any printer made by Google.
+      { "vendorId": 6353, "productId": 19985 },
+      { "vendorId": 6353, "interfaceClass": 7 }
+    ]
+  },
+  ...
+}
+</pre>
+
+<section>
+<h2 id="reference">Reference</h2>
+<p class="api_reference">
+{{+partials.manifest_type
+  type:apis.apps.extensionsManifestTypes.byName.UsbPrinters/}}
+</p>
+</section>