Restore webrtc_base target until r7140 is rolled into Chromium.

In r7140 the webrtc_base target was renamed to rtc_base. This
breaks our FYI bots for rolling WebRTC in Chromium's DEPS.
By re-adding a None target named webrtc_base, this transition
should be smoother.

TBR=henrikg@webrtc.org,
TESTED=Passed build/gyp_chromium on a Chromium checkout with src/third_party/webrtc replaced by a mount like this:
cd /path/to/chromium/src
sudo mount --bind /path/to/webrtc/trunk/webrtc third_party/webrtc

Review URL: https://webrtc-codereview.appspot.com/23589004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7150 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/base/base.gyp

@@ -24,6 +24,16 @@
     }],
   ],
   'targets': [
+    {
+      # Temporary target until Chromium's
+      # src/third_party/libjingle/libjingle.gyp is updated to use rtc_base.
+      # TODO(kjellander): Remove when r7140 is rolled into Chromium's DEPS.
+      'target_name': 'webrtc_base',
+      'type': 'none',
+      'dependencies': [
+        'rtc_base',
+      ],
+    },
     {
       'target_name': 'rtc_base',
       'type': 'static_library',