Use find instead of contains for unordered_map

https://bugs.webkit.org/show_bug.cgi?id=265920

Reviewed by Don Olmstead.

Build fix for PlayStation.
`map.contains(element)` may read nicely, but `map.find(element) != map.end()` is still a one-liner.
Let's stick to the latter for the moment since it's non-trivial to add a new method to an existing STL container.

* Source/WebCore/platform/graphics/SourceBufferPrivate.cpp:
(WebCore::SourceBufferPrivate::addTrackBuffer):
(WebCore::SourceBufferPrivate::validateInitializationSegment):

Canonical link: https://commits.webkit.org/271589@main

Source/WebCore/platform/graphics/SourceBufferPrivate.cpp

@@ -538,7 +538,7 @@ uint64_t SourceBufferPrivate::totalTrackBufferSizeInBytes() const
 
 void SourceBufferPrivate::addTrackBuffer(TrackID trackId, RefPtr<MediaDescription>&& description)
 {
-    ASSERT(!m_trackBufferMap.contains(trackId));
+    ASSERT(m_trackBufferMap.find(trackId) == m_trackBufferMap.end());
 
     m_hasAudio = m_hasAudio || description->isAudio();
     m_hasVideo = m_hasVideo || description->isVideo();
@@ -640,21 +640,21 @@ bool SourceBufferPrivate::validateInitializationSegment(const SourceBufferPrivat
     //   IDs match the ones in the first initialization segment.
     if (segment.audioTracks.size() >= 2) {
         for (auto& audioTrackInfo : segment.audioTracks) {
-            if (!m_trackBufferMap.contains(audioTrackInfo.track->id()))
+            if (m_trackBufferMap.find(audioTrackInfo.track->id()) == m_trackBufferMap.end())
                 return false;
         }
     }
 
     if (segment.videoTracks.size() >= 2) {
         for (auto& videoTrackInfo : segment.videoTracks) {
-            if (!m_trackBufferMap.contains(videoTrackInfo.track->id()))
+            if (m_trackBufferMap.find(videoTrackInfo.track->id()) == m_trackBufferMap.end())
                 return false;
         }
     }
 
     if (segment.textTracks.size() >= 2) {
         for (auto& textTrackInfo : segment.videoTracks) {
-            if (!m_trackBufferMap.contains(textTrackInfo.track->id()))
+            if (m_trackBufferMap.find(textTrackInfo.track->id()) == m_trackBufferMap.end())
                 return false;
         }
     }