Elaborate on Network Service reconnection in README

https://crrev.com/c/2215523 added some more documentation about the
Network Service and how it can crash and recover. This CL aims to
elaborate on this a bit, explaining that if you have a URLLoaderFactory
that you made, it shouldn't just keep working perfectly after the
Network Service is restarted.

R=falken@chromium.org, kinuko@chromium.org, lingqi@chromium.org

Change-Id: I2f28746990eb21805f56862f635860f145088109
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2218310
Commit-Queue: Dominic Farolino <dom@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774983}

services/network/README.md

@@ -74,9 +74,20 @@ the `network::NetworkService` instance.
 # What happens if the network service crashes?
 
 *In the out-of-process case*: If the network service crashes, it gets restarted
-in a new utility process. The goal is for the failure to be mostly recoverable:
-some in-flight requests may fail, but any tabs open will continue to function
-and later requests will succeed.
+in a new utility process. The goal is for the failure to be mostly recoverable.
+It is important to note that any URLLoaderFactories bound to the Network Service
+before it crashes become disconnected, and will no longer continue to work.
+Therefore it is useful to establish reconnection logic if it is detected that
+the URLLoaderFactory is no longer connected.
+
+For example, a navigation request's URLLoaderFactory comes from
+`StoragePartitionImpl::GetURLLoaderFactoryForBrowserProcessInternal` in the
+browser process. This method has logic to detect if the URLLoaderFactory it
+would normally return is disconnected. In that case, it creates a new one which
+is used for all future navigation requests. Since most URLLoaderFactory users
+use factories that are not created out-of-band, and are provided by some
+service, reconnection logic is often implemented for free, and is usually not
+something to worry about.
 
 *In the in-process case*: If the network service crashes in this case, of
 course, the entire browser crashes. This is one reason for the goal to always