Fix a visual flicker when loading chrome://net-export.

Bug: 788668
Change-Id: I9aeb429e91854eecef19cb29dacb65d05465a28f
Reviewed-on: https://chromium-review.googlesource.com/794716Reviewed-by: Helen Li <xunjieli@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519900}

components/net_log/resources/net_export.html

@@ -37,7 +37,7 @@
        * Has controls to start logging.
       =========================================================================
     -->
-    <div id="state-initial">
+    <div id="state-initial" hidden>
       <h2>Capture Network Log</h2>
       <button id="start-logging">Start Logging to Disk</button>
 
@@ -87,7 +87,7 @@
        * Has controls to stop logging
       =========================================================================
     -->
-    <div id="state-logging">
+    <div id="state-logging" hidden>
       <h2>Saving network events to disk...</h2>
 
       <button id="stop-logging">Stop Logging</button>
@@ -113,7 +113,7 @@
        * Has controls to email the log (mobile)
       =========================================================================
     -->
-    <div id="state-stopped">
+    <div id="state-stopped" hidden>
       <h2>Log file written</h2>
 
       <if expr="is_ios or is_android">