Revert "Temporarily remove enable-websocket-auth-connection-reuse from about:flags"

This reverts commit 7e3874d4.

Reason for revert: The flag has now been removed from the about:flags page on M68 where it doesn't work. Re-introduce it in M69 where it works.

Original change's description:
> Temporarily remove enable-websocket-auth-connection-reuse from about:flags
> 
> The M68 branch has a non-working implementation of the
> enable-websocket-auth-connection-reuse flag. In order to avoid the
> confusion of having a flag that works in some versions and not in
> others, temporarily remove the flag from about:flags.
> 
> Once the flag has been disabled in the M68 branch it will be re-enabled
> for M69 by reverting this CL.
> 
> BUG=423609
> 
> Change-Id: Id17ac18e13effcfd5bd946dc1fe0f1c70df96539
> Reviewed-on: https://chromium-review.googlesource.com/1090700
> Commit-Queue: Adam Rice <ricea@chromium.org>
> Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#566730}

TBR=ricea@chromium.org,yhirano@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 423609
Change-Id: Ifb83673ab8e6efaefbbc50e85b560b889fc160ad
Reviewed-on: https://chromium-review.googlesource.com/1107437Reviewed-by: Adam Rice <ricea@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568744}

chrome/browser/about_flags.cc

@@ -3898,6 +3898,11 @@ const FeatureEntry kFeatureEntries[] = {
      FEATURE_VALUE_TYPE(ash::features::kTapVisualizerApp)},
 #endif
 
+    {"enable-websocket-auth-connection-reuse",
+     flag_descriptions::kWebSocketHandshakeReuseConnectionName,
+     flag_descriptions::kWebSocketHandshakeReuseConnectionDescription, kOsAll,
+     FEATURE_VALUE_TYPE(net::WebSocketBasicHandshakeStream::
+                            kWebSocketHandshakeReuseConnection)},
     {"unsafely-treat-insecure-origin-as-secure",
      flag_descriptions::kTreatInsecureOriginAsSecureName,
      flag_descriptions::kTreatInsecureOriginAsSecureDescription, kOsAll,

chrome/browser/flag_descriptions.cc

@@ -1945,6 +1945,13 @@ const char kWebrtcStunOriginDescription[] =
     "When enabled, Stun messages generated by WebRTC will contain the Origin "
     "header.";
 
+const char kWebSocketHandshakeReuseConnectionName[] =
+    "Enable WebSocket connection reuse for authentication";
+const char kWebSocketHandshakeReuseConnectionDescription[] =
+    "Permits the WebSocket handshake to keep the connection open after an "
+    "authentication failure. The connection may be used for further requests "
+    "to send credentials. This is sometimes needed for Windows authentication.";
+
 const char kWebvrName[] = "WebVR";
 const char kWebvrDescription[] =
     "Enables access to experimental Virtual Reality functionality via the "

chrome/browser/flag_descriptions.h

@@ -1183,6 +1183,9 @@ extern const char kWebrtcStunOriginDescription[];
 extern const char kWebrtcH264WithOpenh264FfmpegName[];
 extern const char kWebrtcH264WithOpenh264FfmpegDescription[];
 
+extern const char kWebSocketHandshakeReuseConnectionName[];
+extern const char kWebSocketHandshakeReuseConnectionDescription[];
+
 extern const char kWebvrName[];
 extern const char kWebvrDescription[];