Return a copy of the supported RTP header extensions instead of a reference.

talk/media/webrtc/webrtcvideoengine2.cc

Index: talk/media/webrtc/webrtcvideoengine2.cc
diff --git a/talk/media/webrtc/webrtcvideoengine2.cc b/talk/media/webrtc/webrtcvideoengine2.cc
index 2f0768771154eb182565bffc583eecf06faaa5c6..1178445bffd0fbaf8289a6f58d8d597edeb66438 100644
--- a/talk/media/webrtc/webrtcvideoengine2.cc
+++ b/talk/media/webrtc/webrtcvideoengine2.cc
@@ -556,20 +556,6 @@ WebRtcVideoEngine2::WebRtcVideoEngine2()
       external_encoder_factory_(NULL) {
   LOG(LS_INFO) << "WebRtcVideoEngine2::WebRtcVideoEngine2()";
   video_codecs_ = GetSupportedCodecs();
-  rtp_header_extensions_.push_back(
-      RtpHeaderExtension(kRtpTimestampOffsetHeaderExtension,
-                         kRtpTimestampOffsetHeaderExtensionDefaultId));
-  rtp_header_extensions_.push_back(
-      RtpHeaderExtension(kRtpAbsoluteSenderTimeHeaderExtension,
-                         kRtpAbsoluteSenderTimeHeaderExtensionDefaultId));
-  rtp_header_extensions_.push_back(
-      RtpHeaderExtension(kRtpVideoRotationHeaderExtension,
-                         kRtpVideoRotationHeaderExtensionDefaultId));
-  if (webrtc::field_trial::FindFullName("WebRTC-SendSideBwe") == "Enabled") {
-    rtp_header_extensions_.push_back(RtpHeaderExtension(
-        kRtpTransportSequenceNumberHeaderExtension,
-        kRtpTransportSequenceNumberHeaderExtensionDefaultId));
-  }
 }
 
 WebRtcVideoEngine2::~WebRtcVideoEngine2() {
@@ -617,9 +603,24 @@ const std::vector<VideoCodec>& WebRtcVideoEngine2::codecs() const {
   return video_codecs_;
 }
 
-const std::vector<RtpHeaderExtension>&
-WebRtcVideoEngine2::rtp_header_extensions() const {
-  return rtp_header_extensions_;
+std::vector<RtpHeaderExtension>
+WebRtcVideoEngine2::SupportedRtpHeaderExtensions() const {
+  std::vector<RtpHeaderExtension> rtp_header_extensions;
+  rtp_header_extensions.push_back(
+      RtpHeaderExtension(kRtpTimestampOffsetHeaderExtension,
+                         kRtpTimestampOffsetHeaderExtensionDefaultId));
+  rtp_header_extensions.push_back(
+      RtpHeaderExtension(kRtpAbsoluteSenderTimeHeaderExtension,
+                         kRtpAbsoluteSenderTimeHeaderExtensionDefaultId));
+  rtp_header_extensions.push_back(
+      RtpHeaderExtension(kRtpVideoRotationHeaderExtension,
+                         kRtpVideoRotationHeaderExtensionDefaultId));
+  if (webrtc::field_trial::FindFullName("WebRTC-SendSideBwe") == "Enabled") {
+    rtp_header_extensions.push_back(RtpHeaderExtension(
+        kRtpTransportSequenceNumberHeaderExtension,
+        kRtpTransportSequenceNumberHeaderExtensionDefaultId));
+  }
+  return rtp_header_extensions;
 }
 
 void WebRtcVideoEngine2::SetExternalDecoderFactory(