Move net-export thread-hopping code into NetLogFileWriter and add IO polled data.

components/net_log/resources/net_export.js

Index: components/net_log/resources/net_export.js
diff --git a/components/net_log/resources/net_export.js b/components/net_log/resources/net_export.js
index 442379d305ccc41920fe3cbd0e400096497cf81d..73da23aefa2456954b85ee0cb612b97c3c168214 100644
--- a/components/net_log/resources/net_export.js
+++ b/components/net_log/resources/net_export.js
@@ -106,19 +106,19 @@ var NetExportView = (function() {
         $('export-view-start-data').disabled = false;
 
         // If there's an existing log, allow sending it.
-        if (exportNetLogInfo.logType != 'NONE') {
+        if (!!exportNetLogInfo.logExists) {

[eroman, 2017/01/06 21:46:23]

Agreed these names are clearer!

           $('export-view-deletes-log-text').hidden = false;
           $('export-view-send-data').disabled = false;
-          if (exportNetLogInfo.logType == 'UNKNOWN') {
+          if (!exportNetLogInfo.logCaptureModeKnown) {
             $('export-view-send-old-log-text').hidden = false;
-          } else if (exportNetLogInfo.logType == 'NORMAL') {
+          } else if (exportNetLogInfo.captureMode == 'NORMAL') {
             $('export-view-private-data-text').hidden = false;
           }
         }
       } else if (exportNetLogInfo.state == 'LOGGING') {
         // Only possible to stop logging. Radio buttons reflects current state.
         document.querySelector('input[name="log-mode"][value="' +
-                               exportNetLogInfo.logType + '"]').checked = true;
+            exportNetLogInfo.captureMode + '"]').checked = true;
         $('export-view-stop-data').disabled = false;
       } else if (exportNetLogInfo.state == 'UNINITIALIZED') {
         $('export-view-file-path-text').textContent =