Change on-device example to use the origin trial API (#1337)

* Add scaffolding for Prompt API OT example

* Rewrite existing example to use the OT

* Add trial token and key

* Update error message, add `minimum_chrome_version`

* Fix feature detection

* Some README refinements

* Correct instructions

* OT refinement

functional-samples/ai.gemini-on-device/README.md

@@ -1,14 +1,21 @@
 # On-device AI with Gemini Nano
 
-This sample demonstrates how to use the experimental Gemini Nano API in Chrome. To learn more about the API and how to sign-up for the preview, head over to [Built-in AI on developer.chrome.com](https://developer.chrome.com/docs/ai/built-in).
+This sample demonstrates how to use the experimental Gemini Nano API available in the context of an origin trial in Chrome with Chrome Extensions. To learn more about the API and how to sign-up for the origin trial, head over to [Built-in AI on developer.chrome.com](https://developer.chrome.com/docs/ai/built-in).
 
 ## Overview
 
-The extension provides a chat interface using the prompt API with Chrome's built-in Gemini Nano model.
+The extension provides a chat interface using the Prompt API with Chrome's built-in Gemini Nano model.
 
 ## Running this extension
 
 1. Clone this repository.
-2. Load this directory in Chrome as an [unpacked extension](https://developer.chrome.com/docs/extensions/mv3/getstarted/development-basics/#load-unpacked).
-3. Click the extension icon.
-4. Interact with the prompt API in the sidebar.
+1. Launch Chrome with the following flag, which makes sure the origin trial token in `manifest.json` is accepted by the browser. This won't be necessary once the origin trial is live.
+
+   `--origin-trial-public-key=dRCs+TocuKkocNKa0AtZ4awrt9XKH2SQCI6o4FY6BNA=`
+1. Load this directory in Chrome as an [unpacked extension](https://developer.chrome.com/docs/extensions/mv3/getstarted/development-basics/#load-unpacked).
+1. Click the extension icon.
+1. Interact with the Prompt API in the sidebar.
+
+## Creating your own extension
+
+If you use this sample as the foundation for your own extension, be sure to update the `"trial_tokens"` field [with your own origin trial token](https://developer.chrome.com/docs/web-platform/origin-trials?hl=en#extensions) and to remove the `"key"` field in `manifest.json`.

functional-samples/ai.gemini-on-device/manifest.json

@@ -6,7 +6,10 @@
   "background": {
     "service_worker": "background.js"
   },
-  "permissions": ["sidePanel"],
+  "permissions": ["sidePanel", "aiLanguageModelOriginTrial"],
+  "trial_tokens": ["A6hC1yvazc5QTqSESgEo3uwIUs1KBM4VB93yiTdtgFlFlYNJjf18zmzScpaCepaYpNLaMJ4dNkDps+vbrk7oEw8AAAB9eyJvcmlnaW4iOiAiY2hyb21lLWV4dGVuc2lvbjovL2lkZm1qYmJqY21qamtoYWlvZmltbWNtY29qYmlnbmpmIiwgImZlYXR1cmUiOiAiQUlQcm9tcHRBUElGb3JFeHRlbnNpb24iLCAiZXhwaXJ5IjogMTk4OTQwNzUwMH0="],
+  "key": "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAi99ZKuRYfZMQ80XryBYKNA4DJTHPMEiNkiF6TLqTXMp4Cb23I/DTblxlEELWyM1vDuXeFI7jqXDuM6YVHd7zTtA1hGbGgLm9w9+d763x2wCRbxud+dXIXW4IoD4CqXpCLscDD7Vrar/I5XbcmdA9jjlCXMGS2OKNRhYMjNpaVhFCi2jzWid+92DZSpPbdM9iBODGfwnFNp16tFX8/dDx3w23FneeOVHV3JjNIWO3uT60AhZWOtcQlERuMBJmEkKAgqE8T3ZjoZe4ALupfvDxI7khP29+gBXhgF/r6T0RAbB1LfxubhyLk/X7aC/sw3umCemqvc+knvKRBLHMVl1nHQIDAQAB",
+  "minimum_chrome_version": "131",
   "side_panel": {
     "default_path": "sidepanel/index.html"
   },

functional-samples/ai.gemini-on-device/sidepanel/index.js

@@ -14,7 +14,7 @@ let session;
 async function runPrompt(prompt, params) {
   try {
     if (!session) {
-      session = await window.ai.languageModel.create(params);
+      session = await chrome.aiOriginTrial.languageModel.create(params);
     }
     return session.prompt(prompt);
   } catch (e) {
@@ -35,11 +35,11 @@ async function reset() {
 }
 
 async function initDefaults() {
-  if (!window.ai) {
-    showResponse('Error: window.ai not supported in this browser');
+  if (!('aiOriginTrial' in chrome)) {
+    showResponse('Error: chrome.aiOriginTrial not supported in this browser');
     return;
   }
-  const defaults = await window.ai.languageModel.capabilities();
+  const defaults = await chrome.aiOriginTrial.languageModel.capabilities();
   console.log('Model default:', defaults);
   sliderTemperature.value = defaults.temperature;
   sliderTopK.value = defaults.topK;