Replace labs with std::abs.

Resolves clang 3.5 warnings on OS X for -Wabsolute-value.

BUG=chromium:351479
R=andrew@webrtc.org, thakis@chromium.org

Review URL: https://webrtc-codereview.appspot.com/9869004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5692 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/modules/video_coding/main/source/receiver.cc b/webrtc/modules/video_coding/main/source/receiver.cc
index e3fc0ce..261c51e 100644
--- a/webrtc/modules/video_coding/main/source/receiver.cc
+++ b/webrtc/modules/video_coding/main/source/receiver.cc
@@ -156,12 +156,12 @@
   // Assume that render timing errors are due to changes in the video stream.
   if (next_render_time_ms < 0) {
     timing_error = true;
-  } else if (labs(next_render_time_ms - now_ms) > max_video_delay_ms_) {
+  } else if (std::abs(next_render_time_ms - now_ms) > max_video_delay_ms_) {
     WEBRTC_TRACE(webrtc::kTraceWarning, webrtc::kTraceVideoCoding,
                  VCMId(vcm_id_, receiver_id_),
                  "This frame is out of our delay bounds, resetting jitter "
                  "buffer: %d > %d",
-                 static_cast<int>(labs(next_render_time_ms - now_ms)),
+                 static_cast<int>(std::abs(next_render_time_ms - now_ms)),
                  max_video_delay_ms_);
     timing_error = true;
   } else if (static_cast<int>(timing_->TargetVideoDelay()) >