Revert 7184 "Enable ipv6 by default for webrtc under a Finch exp..."

Breaks Chrome build and prevents rolling WebRTC into Chrome DEPS.

> Enable ipv6 by default for webrtc under a Finch experiment.
> 
> BUG=413437 (chromium)
> https://code.google.com/p/chromium/issues/detail?id=413437
> 
> Review URL: https://webrtc-codereview.appspot.com/23529005

TBR=guoweis@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/30399004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7190 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/talk/app/webrtc/peerconnection.cc b/talk/app/webrtc/peerconnection.cc
index d133889..3698381 100644
--- a/talk/app/webrtc/peerconnection.cc
+++ b/talk/app/webrtc/peerconnection.cc
@@ -39,9 +39,6 @@
 #include "talk/session/media/channelmanager.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/stringencode.h"
-#ifdef WEBRTC_CHROMIUM_BUILD
-#include "webrtc/system_wrappers/interface/field_trial.h"
-#endif
 
 namespace {
 
@@ -356,19 +353,12 @@
                             cricket::PORTALLOCATOR_ENABLE_SHARED_UFRAG |
                             cricket::PORTALLOCATOR_ENABLE_SHARED_SOCKET;
   bool value;
-  // If IPv6 flag was specified, we'll not override it by experiment.
   if (FindConstraint(
-          constraints, MediaConstraintsInterface::kEnableIPv6, &value, NULL)) {
-    if (value) {
-      portallocator_flags |= cricket::PORTALLOCATOR_ENABLE_IPV6;
-    }
-  }
-#ifdef WEBRTC_CHROMIUM_BUILD
-  else if (webrtc::field_trial::FindFullName("WebRTC-IPv6Default") ==
-           "Enabled") {
+        constraints,
+        MediaConstraintsInterface::kEnableIPv6,
+        &value, NULL) && value) {
     portallocator_flags |= cricket::PORTALLOCATOR_ENABLE_IPV6;
   }
-#endif  // WEBRTC_CHROMIUM_BUILD
 
   port_allocator_->set_flags(portallocator_flags);
   // No step delay is used while allocating ports.