Clarify the Testing section of the origin trials documentation.

This makes it more obvious that generate_token.py is to be used in
conjunction with --origin-trial-public-key.

Change-Id: Ia6fc0c17519013804c10461c3d41cc9323bbb16c
Reviewed-on: https://chromium-review.googlesource.com/c/1412808
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622989}

docs/origin_trials_integration.md

@@ -99,29 +99,30 @@ from the renderer.
 
 ## Testing
 
-If you want to test your code's interactions with the framework, you'll need to
-generate some tokens of your own. To generate your own tokens, use
-[generate_token.py]. You can generate signed tokens for localhost, or for
-127.0.0.1, or for any origin that you need to help you test. For example:
+To test an origin trial feature during development, follow these steps:
 
-```
-tools/origin_trials/generate_token.py http://localhost:8000 MyFeature
-```
+1. Use [generate_token.py] to generate a token signed with the test private key.
+   You can generate signed tokens for any origin that you need to help you test,
+   including localhost or 127.0.0.1. Example:
 
-The file `tools/origin_trials/eftest.key` is used by default as the private key
-for the test keypair used by Origin Trials unit tests and web tests (i.e. in
-content shell). Tokens generated with this key will **not** work in the browser
-by default (see the [Developer Guide] for instructions on creating real tokens).
-To use a test token with the browser, run Chrome with the command-line flag:
+      ```
+      tools/origin_trials/generate_token.py http://localhost:8000 MyFeature
+      ```
 
-```
---origin-trial-public-key=dRCs+TocuKkocNKa0AtZ4awrt9XKH2SQCI6o4FY6BNA=
-```
+2. Copy the token from the end of the output and use it in a `<meta>` tag or
+   an `Origin-Trial` header as described in the [Developer Guide].
 
-This is the base64 encoding of the public key associated with `eftest.key`. If
-it doesn't work, see [trial_token_unittest.cc]. If you cannot set command-line
-switches (e.g., on Chrome OS), you can also directly modify
-[chrome_origin_trial_policy.cc].
+3. Run Chrome with the test public key by passing:
+   `--origin-trial-public-key=dRCs+TocuKkocNKa0AtZ4awrt9XKH2SQCI6o4FY6BNA=`
+
+The `--origin-trial-public-key` switch is not needed with `content_shell`, as it
+uses the test public key by default.
+
+The test private key is stored in the repo at `tools/origin_trials/eftest.key`.
+It's also used by Origin Trials unit tests and web tests.
+
+If you cannot set command-line switches (e.g., on Chrome OS), you can also
+directly modify [chrome_origin_trial_policy.cc].
 
 ### Web Tests
 When using the \[OriginTrialEnabled\] IDL attribute, you should add web tests