Use a different description for chrome://net-export on iOS.

Chrome on iOS does not use //net for issuing network requests for web content,
making the data captured by chrome://net-export/ more limited.

Bug: 1140996
Change-Id: I46f9d0d986672a9a10b7e8bd2f5b82145525002c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490270Reviewed-by: Eric Lawrence [MSFT] <ericlaw@microsoft.com>
Reviewed-by: Eric Roman <eroman@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Auto-Submit: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821886}

components/net_log/resources/net_export.html

@@ -44,9 +44,17 @@
 
       <div class="section-container">
         Click the button to start logging future network activity to a file on
-        disk. The log includes details of network activity from all of Chrome,
+        disk.
+        <if expr="not(is_ios)">
+        The log includes details of network activity from all of Chrome,
         including incognito and non-incognito tabs, visited URLs, and
         information about the network configuration.
+        </if>
+        <if expr="is_ios">
+        The log includes details of network activity handled by Chrome's
+        internal network stack. Note, this does not include network requests
+        for ordinary web content, which are instead handled by WKWebView.
+        </if>
         <a href="https://dev.chromium.org/for-testers/providing-network-details"
            target="_blank">
         See the Chromium website for more detailed instructions.</a>