Update the System.Runtime and System.Memory ref based on new buildtools (#28906)

* Update the System.Runtime and System.Memory ref based on new buildtools

* Fix HttpContent TryGetBuffer and update System.Runtime ref

* Update System.Memory ref and fix PipeAwaitable (assign CancellationTokenRegistration)

* Fix 'use of unassigned local' error in System.Memory performance tests

Author: ahsonkhan

src/System.IO.Pipelines/src/System/IO/Pipelines/PipeAwaitable.cs

@@ -29,6 +29,7 @@ public PipeAwaitable(bool completed, bool useSynchronizationContext)
             _canceledState = CanceledState.NotCanceled;
             _completion = completed ? s_awaitableIsCompleted : s_awaitableIsNotCompleted;
             _completionState = null;
+            _cancellationTokenRegistration = default;
             _synchronizationContext = null;
             _executionContext = null;
             _useSynchronizationContext = useSynchronizationContext;
@@ -41,7 +42,7 @@ public PipeAwaitable(bool completed, bool useSynchronizationContext)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public CancellationTokenRegistration AttachToken(CancellationToken cancellationToken, Action<object> callback, object state)
         {
-            CancellationTokenRegistration oldRegistration;
+            CancellationTokenRegistration oldRegistration = default;
             if (!cancellationToken.Equals(_cancellationToken))
             {
                 oldRegistration = _cancellationTokenRegistration;

src/System.Memory/ref/System.Memory.cs

@@ -92,6 +92,7 @@ public static void Reverse<T>(this System.Span<T> span) { }
     public readonly partial struct Memory<T>
     {
         private readonly object _dummy;
+        private readonly int _dummyPrimitive;
         public Memory(System.Buffers.MemoryManager<T> manager, int start, int length) { throw null; }
         public Memory(T[] array) { throw null; }
         public Memory(T[] array, int start, int length) { throw null; }
@@ -120,6 +121,7 @@ public void CopyTo(System.Memory<T> destination) { }
     public readonly partial struct ReadOnlyMemory<T>
     {
         private readonly object _dummy;
+        private readonly int _dummyPrimitive;
         public ReadOnlyMemory(T[] array) { throw null; }
         public ReadOnlyMemory(T[] array, int start, int length) { throw null; }
         public static System.ReadOnlyMemory<T> Empty { get { throw null; } }
@@ -144,6 +146,7 @@ public void CopyTo(System.Memory<T> destination) { }
     public readonly ref partial struct ReadOnlySpan<T>
     {
         private readonly object _dummy;
+        private readonly int _dummyPrimitive;
         [System.CLSCompliantAttribute(false)]
         public unsafe ReadOnlySpan(void* pointer, int length) { throw null; }
         public ReadOnlySpan(T[] array) { throw null; }
@@ -172,13 +175,15 @@ public void CopyTo(System.Span<T> destination) { }
         public ref partial struct Enumerator
         {
             private object _dummy;
+            private int _dummyPrimitive;
             public ref readonly T Current { get { throw null; } }
             public bool MoveNext() { throw null; }
         }
     }
     public readonly partial struct SequencePosition : System.IEquatable<System.SequencePosition>
     {
         private readonly object _dummy;
+        private readonly int _dummyPrimitive;
         public SequencePosition(object @object, int integer) { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute((System.ComponentModel.EditorBrowsableState)(1))]
         public override bool Equals(object obj) { throw null; }
@@ -195,6 +200,7 @@ public ref partial struct Enumerator
     public readonly ref partial struct Span<T>
     {
         private readonly object _dummy;
+        private readonly int _dummyPrimitive;
         [System.CLSCompliantAttribute(false)]
         public unsafe Span(void* pointer, int length) { throw null; }
         public Span(T[] array) { throw null; }
@@ -226,6 +232,7 @@ public void Fill(T value) { }
         public ref partial struct Enumerator
         {
             private object _dummy;
+            private int _dummyPrimitive;
             public ref T Current { get { throw null; } }
             public bool MoveNext() { throw null; }
         }
@@ -258,6 +265,7 @@ public partial interface IPinnable
     public partial struct MemoryHandle : System.IDisposable
     {
         private object _dummy;
+        private int _dummyPrimitive;
         [System.CLSCompliantAttribute(false)]
         public unsafe MemoryHandle(void* pointer, System.Runtime.InteropServices.GCHandle handle = default(System.Runtime.InteropServices.GCHandle), System.Buffers.IPinnable pinnable = null) { throw null; }
         [System.CLSCompliantAttribute(false)]
@@ -302,6 +310,7 @@ protected ReadOnlySequenceSegment() { }
     public readonly partial struct ReadOnlySequence<T>
     {
         private readonly object _dummy;
+        private readonly int _dummyPrimitive;
         public static readonly System.Buffers.ReadOnlySequence<T> Empty;
         public ReadOnlySequence(System.Buffers.ReadOnlySequenceSegment<T> startSegment, int startIndex, System.Buffers.ReadOnlySequenceSegment<T> endSegment, int endIndex) { throw null; }
         public ReadOnlySequence(System.ReadOnlyMemory<T> memory) { throw null; }
@@ -330,14 +339,15 @@ public readonly partial struct ReadOnlySequence<T>
         public partial struct Enumerator
         {
             private object _dummy;
+            private int _dummyPrimitive;
             public Enumerator(in System.Buffers.ReadOnlySequence<T> sequence) { throw null; }
             public System.ReadOnlyMemory<T> Current { get { throw null; } }
             public bool MoveNext() { throw null; }
         }
     }
     public readonly partial struct StandardFormat : System.IEquatable<System.Buffers.StandardFormat>
     {
-        private readonly int _dummy;
+        private readonly int _dummyPrimitive;
         public const byte MaxPrecision = (byte)99;
         public const byte NoPrecision = (byte)255;
         public StandardFormat(char symbol, byte precision = (byte)255) { throw null; }

src/System.Memory/tests/Performance/Perf.Memory.Slice.cs

@@ -123,7 +123,7 @@ private static void ReadOnlyMemory_Char_GetSpanThenSlice(int numberOfChars)
         public static void ReadOnlyMemory_Byte_TryGetArray()
         {
             ReadOnlyMemory<byte> memory = new byte[1];
-            ArraySegment<byte> result;
+            ArraySegment<byte> result = default;
 
             foreach (BenchmarkIteration iteration in Benchmark.Iterations)
             {
@@ -144,7 +144,7 @@ public static void ReadOnlyMemory_Byte_TryGetArray()
         public static void ReadOnlyMemory_Char_TryGetArray()
         {
             ReadOnlyMemory<char> memory = new char[1];
-            ArraySegment<char> result;
+            ArraySegment<char> result = default;
 
             foreach (BenchmarkIteration iteration in Benchmark.Iterations)
             {

src/System.Net.Http/src/System/Net/Http/HttpContent.cs

@@ -143,7 +143,12 @@ internal void SetBuffer(byte[] buffer, int offset, int count)
 
         internal bool TryGetBuffer(out ArraySegment<byte> buffer)
         {
-            return _bufferedContent != null && _bufferedContent.TryGetBuffer(out buffer);
+            if (_bufferedContent != null)
+            {
+                return _bufferedContent.TryGetBuffer(out buffer);
+            }
+            buffer = default;
+            return false;
         }
 
         protected HttpContent()