Replace scoped_ptr with unique_ptr in webrtc/call/

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1789903003

Cr-Commit-Position: refs/heads/master@{#11970}
diff --git a/webrtc/call/call_unittest.cc b/webrtc/call/call_unittest.cc
index 75c8238..0da91a9 100644
--- a/webrtc/call/call_unittest.cc
+++ b/webrtc/call/call_unittest.cc
@@ -9,6 +9,7 @@
  */
 
 #include <list>
+#include <memory>
 
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -31,7 +32,7 @@
 
  private:
   testing::NiceMock<webrtc::test::MockVoiceEngine> voice_engine_;
-  rtc::scoped_ptr<webrtc::Call> call_;
+  std::unique_ptr<webrtc::Call> call_;
 };
 }  // namespace