Declare the Clone operator of SessionDescriptionInterface as const.

Bug: webrtc:12215
Change-Id: I8e44e2b9365893ecf481e69060771c2c208bbcdf
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/198125
Reviewed-by: Markus Handell <handellm@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32858}

api/jsep.h

diff --git a/api/jsep.h b/api/jsep.h
index 7ef4c53..dcf8213 100644
--- a/api/jsep.h
+++ b/api/jsep.h
@@ -139,7 +139,7 @@
   // Create a new SessionDescriptionInterface object
   // with the same values as the old object.
   // TODO(bugs.webrtc.org:12215): Remove default implementation
-  virtual std::unique_ptr<SessionDescriptionInterface> Clone() {
+  virtual std::unique_ptr<SessionDescriptionInterface> Clone() const {
     return nullptr;
   }
 

api/jsep_session_description.h

diff --git a/api/jsep_session_description.h b/api/jsep_session_description.h
index 0ba3807..e13d85e 100644
--- a/api/jsep_session_description.h
+++ b/api/jsep_session_description.h
@@ -49,7 +49,7 @@
                   const std::string& session_id,
                   const std::string& session_version);
 
-  virtual std::unique_ptr<SessionDescriptionInterface> Clone();
+  virtual std::unique_ptr<SessionDescriptionInterface> Clone() const;
 
   virtual cricket::SessionDescription* description() {
     return description_.get();

pc/jsep_session_description.cc

diff --git a/pc/jsep_session_description.cc b/pc/jsep_session_description.cc
index 2334e92..e0b2311 100644
--- a/pc/jsep_session_description.cc
+++ b/pc/jsep_session_description.cc
@@ -215,7 +215,8 @@
   return true;
 }
 
-std::unique_ptr<SessionDescriptionInterface> JsepSessionDescription::Clone() {
+std::unique_ptr<SessionDescriptionInterface> JsepSessionDescription::Clone()
+    const {
   auto new_description = std::make_unique<JsepSessionDescription>(type_);
   new_description->Initialize(description_->Clone(), session_id_,
                               session_version_);