[AW][Dev-UI] misc docs updates

No change to logic, only docs. This updates the commandline docs to
point to Developer UI in more spots and to remove a reference to the log
verbosifier app.

This removes a "new in M84" aside for a Dev UI feature which was
cherry-picked to M83.

This adds documentation for flag persistence and "check for WebView
updates," both of which were added in M84.

Fixed: 1058571
Test: tools/md_browser/md_browser.py
Test: Upload to gerrit > open file > click "gitiles"
Change-Id: Ia796cd84d3556fa15d6b251d18b55cde546d0609
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2186750
Commit-Queue: Hazem Ashmawy <hazems@chromium.org>
Auto-Submit: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Hazem Ashmawy <hazems@chromium.org>
Cr-Commit-Position: refs/heads/master@{#766462}

android_webview/docs/commandline-flags.md

@@ -3,11 +3,12 @@
 ## Can I apply commandline flags on my device?
 
 *** note
-**Note:** WebView only permits toggling arbitrary commandline flags on devices/emulators
-running a debuggable Android OS image. **Most users cannot follow these
-instructions**, because they're using devices with production Android images.
+**Note:** this guide only applies to userdebug/eng devices and emulators. Most
+users and app developers **do not** have debuggable devices, and therefore
+cannot follow this guide.
 
-If you need to toggle flags on **production devices**, see [this guide](flag-ui.md).
+If you need to toggle flags on production Android devices, you can use [WebView
+DevTools](developer-ui.md).
 ***
 
 You can check which Android image you have on your device with the following:
@@ -18,15 +19,17 @@ You can check which Android image you have on your device with the following:
 $ source build/android/envsetup.sh
 
 # If this outputs "userdebug" or "eng" then you can apply flags following this
-# guide. If it outputs "user" then you cannot apply flags on this device.
+# guide. If it outputs "user" then you can only use WebView DevTools.
 $ adb shell getprop ro.build.type
 userdebug
 ```
 
-If the above outputs "user," then you **cannot** apply flags on the
-device/emulator. If you intend to use this device for chromium development, then
-you may consider [re-flashing the device or creating a debuggable Android
-emulator](device-setup.md).
+If the above outputs "user," then you have two options:
+
+* Try using [WebView DevTools](developer-ui.md) to toggle flags (also works on
+  userdebug and eng devices)
+* Reflash your device or create a debuggable emulator (see [device
+  setup](device-setup.md))
 
 ## Applying flags
 
@@ -93,10 +96,13 @@ adb shell "cat ${FLAG_FILE}"
 
 ## Verifying flags are applied
 
-You can confirm you've applied commandline flags correctly by dumping the full
-state of the commandline flags with the [WebView Log Verbosifier
-app](/android_webview/tools/webview_log_verbosifier/README.md) and starting up a
-WebView app.
+You can add the `--webview-verbose-logging` flag, which tells WebView to dump
+its full commandline and variations state to logs during startup. You can filter
+device logs with:
+
+```shell
+adb logcat | grep -iE 'Active field trial|WebViewCommandLine'
+```
 
 ## Applying Features with flags
 

android_webview/docs/developer-ui.md

@@ -112,6 +112,14 @@ When you're done, open the notification tray and tap the WebView DevTools
 notification to go back to the flag UI. Tap "Reset all to default" and kill and
 restart WebView apps to go back to the default behavior.
 
+*** aside
+[Starting in
+M84](https://chromiumdash.appspot.com/commit/f5ee8b7f1d23d2a915ea234bdd4e49e4c908b267),
+toggled flags will be restored after WebView updates or rebooting your device.
+This is convenient if you want to try out features for longer periods of time,
+such as for dogfooding or compatibility testing.
+***
+
 ### Overriding variations/Field Trials
 
 Like Chrome, WebView supports A/B experiments and feature rollouts through
@@ -176,10 +184,6 @@ system UI where you can select your new WebView channel.
 
 ### Filing a bug report
 
-*** aside
-This was [added in M84](https://chromiumdash.appspot.com/commit/874adae46ba404dfec1660ef239899eef47d72bc).
-***
-
 You can file general bug reports for the WebView engineering team. Launch
 WebView DevTools, open the three-dotted menu, and select "Report WebView Bug."
 Similar to filing bug reports for crashes, this will open the system browser to
@@ -187,6 +191,16 @@ Similar to filing bug reports for crashes, this will open the system browser to
 tracker](https://bugs.chromium.org/p/chromium/issues/entry?template=Webview+Bugs&labels=Via-WebView-DevTools)
 (requires sign-in), where you can describe the issue.
 
+### Check for WebView updates
+
+*** aside
+This was [added in M84](https://chromiumdash.appspot.com/commit/f23d4aa70857ce71a44a2341584461feae95b8a6).
+***
+
+You can check for WebView updates directly from WebView DevTools. This is handy
+if you've applied flags, since the Play Store may pause automatic updates while
+WebView's persistent service is running.
+
 ## Looking for Chrome DevTools?
 
 You can debug WebView even more with Chrome DevTools! For detailed instructions,