Modernize equality operators in //services

This CL is pure clean-up and contains no functionality changes.
Depending on the files covered in the CL (since the CL was generated
using git cl split), it does a subset of the following:
the following:
- Remove unneeded operator!= declarations/definitions since C++20 can
  automatically derive those from operator==.
- Default operator== where this is equivalent to the current behavior.
- Default operator<=> where this is equivalent to the current
  behavior.

This CL was uploaded by git cl split.

R=steimel@chromium.org

Bug: 40256175
Change-Id: Ice095859dc878a0e2c6b78b9d40274f5a9fabe4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6540427
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Auto-Submit: Jan Keitel <jkeitel@google.com>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1459507}

services/media_session/public/cpp/media_metadata.cc

@@ -15,16 +15,6 @@ MediaMetadata::~MediaMetadata() = default;
 
 MediaMetadata::MediaMetadata(const MediaMetadata& other) = default;
 
-bool MediaMetadata::operator==(const MediaMetadata& other) const {
-  return title == other.title && artist == other.artist &&
-         album == other.album && source_title == other.source_title &&
-         chapters == other.chapters;
-}
-
-bool MediaMetadata::operator!=(const MediaMetadata& other) const {
-  return !(*this == other);
-}
-
 bool MediaMetadata::IsEmpty() const {
   return title.empty() && artist.empty() && album.empty() &&
          source_title.empty() && chapters.empty();

services/media_session/public/cpp/media_metadata.h

@@ -31,8 +31,7 @@ struct COMPONENT_EXPORT(MEDIA_SESSION_BASE_CPP) MediaMetadata {
 
   MediaMetadata(const MediaMetadata& other);
 
-  bool operator==(const MediaMetadata& other) const;
-  bool operator!=(const MediaMetadata& other) const;
+  friend bool operator==(const MediaMetadata&, const MediaMetadata&) = default;
 
 #if BUILDFLAG(IS_ANDROID)
   // Creates a Java MediaMetadata instance and returns the JNI ref.

services/media_session/public/cpp/media_position.cc

@@ -79,10 +79,6 @@ bool MediaPosition::operator==(const MediaPosition& other) const {
   return GetPositionAtTime(now) == other.GetPositionAtTime(now);
 }
 
-bool MediaPosition::operator!=(const MediaPosition& other) const {
-  return !(*this == other);
-}
-
 std::string MediaPosition::ToString() const {
   return base::StringPrintf(
       "playback_rate=%f duration=%f current_time=%f end_of_media=%s",

services/media_session/public/cpp/media_position.h

@@ -76,7 +76,6 @@ struct COMPONENT_EXPORT(MEDIA_SESSION_BASE_CPP) MediaPosition {
   base::TimeDelta GetPositionAtTime(base::TimeTicks time) const;
 
   bool operator==(const MediaPosition&) const;
-  bool operator!=(const MediaPosition&) const;
 
   std::string ToString() const;