Remove all remaining non-test uses of std::stringstream.

Bug: webrtc:8982
Change-Id: I635a8545c46dc8c89663d64af351e22e65cbcb33
Reviewed-on: https://webrtc-review.googlesource.com/98880
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24715}
diff --git a/api/rtcerror.h b/api/rtcerror.h
index c87ce91..4910682 100644
--- a/api/rtcerror.h
+++ b/api/rtcerror.h
@@ -86,12 +86,9 @@
   // Creates a "no error" error.
   RTCError() {}
   explicit RTCError(RTCErrorType type) : type_(type) {}
-  // For performance, prefer using the constructor that takes a const char* if
-  // the message is a static string.
-  RTCError(RTCErrorType type, const char* message)
-      : type_(type), static_message_(message), have_string_message_(false) {}
-  RTCError(RTCErrorType type, std::string&& message)
-      : type_(type), string_message_(message), have_string_message_(true) {}
+
+  RTCError(RTCErrorType type, std::string message)
+      : type_(type), message_(std::move(message)) {}
 
   // Delete the copy constructor and assignment operator; there aren't any use
   // cases where you should need to copy an RTCError, as opposed to moving it.
@@ -103,8 +100,6 @@
   RTCError(RTCError&& other);
   RTCError& operator=(RTCError&& other);
 
-  ~RTCError();
-
   // Identical to default constructed error.
   //
   // Preferred over the default constructor for code readability.
@@ -118,10 +113,8 @@
   // anything but logging/diagnostics, since messages are not guaranteed to be
   // stable.
   const char* message() const;
-  // For performance, prefer using the method that takes a const char* if the
-  // message is a static string.
-  void set_message(const char* message);
-  void set_message(std::string&& message);
+
+  void set_message(std::string message);
 
   // Convenience method for situations where you only care whether or not an
   // error occurred.
@@ -129,16 +122,7 @@
 
  private:
   RTCErrorType type_ = RTCErrorType::NONE;
-  // For performance, we use static strings wherever possible. But in some
-  // cases the error string may need to be constructed, in which case an
-  // std::string is used.
-  union {
-    const char* static_message_ = "";
-    std::string string_message_;
-  };
-  // Whether or not |static_message_| or |string_message_| is being used in the
-  // above union.
-  bool have_string_message_ = false;
+  std::string message_;
 };
 
 // Outputs the error as a friendly string. Update this method when adding a new