Add a chrome://flags entry for --log-net-log and use a default path.

If no value for the --log-net-log command line switch is given,
default to netlog.json in the user data directory. The chrome://flags
entry also enables logging to that file.

This makes it easier to enable network logging during startup on
platforms where changing command line flags is difficult, e.g. Android
or Chrome OS.

Change-Id: Ibb2e3036242cc2f927a7d789773a155d1c905d39
Reviewed-on: https://chromium-review.googlesource.com/750963
Commit-Queue: Bernhard Bauer <[email protected]>
Reviewed-by: Jochen Eisinger <[email protected]>
Cr-Commit-Position: refs/heads/master@{#514169}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 82f11ce..8d001f8 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -280,6 +280,9 @@
 extern const char kEnableNavigationTracingName[];
 extern const char kEnableNavigationTracingDescription[];
 
+extern const char kEnableNetworkLoggingToFileName[];
+extern const char kEnableNetworkLoggingToFileDescription[];
+
 extern const char kEnableNetworkServiceName[];
 extern const char kEnableNetworkServiceDescription[];