Adding support for HttpHandlerDiagnosticListener.

src/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSource.cs

@@ -14,7 +14,7 @@ public virtual void Dispose() { }
     public bool IsEnabled() { throw null; }
     public override bool IsEnabled(string name) { throw null; }
     public override bool IsEnabled(string name, object arg1, object arg2 = null) { throw null; }
-    public System.IDisposable Subscribe(System.IObserver<System.Collections.Generic.KeyValuePair<string, object>> observer) { throw null; }
+    public virtual System.IDisposable Subscribe(System.IObserver<System.Collections.Generic.KeyValuePair<string, object>> observer) { throw null; }
     public virtual System.IDisposable Subscribe(System.IObserver<System.Collections.Generic.KeyValuePair<string, object>> observer, System.Predicate<string> isEnabled) { throw null; }
     public virtual System.IDisposable Subscribe(System.IObserver<System.Collections.Generic.KeyValuePair<string, object>> observer, System.Func<string, object, object, bool> isEnabled) { throw null; }
     public override void Write(string name, object parameters) { }

src/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj

@@ -18,6 +18,12 @@
   <PropertyGroup Condition="'$(TargetGroup)' == 'net45' OR '$(TargetGroup)' == 'net46' OR '$(TargetGroup)' == 'netfx'">
     <DefineConstants>$(DefineConstants);ALLOW_PARTIALLY_TRUSTED_CALLERS</DefineConstants>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(TargetGroup)' == 'net46'">
+    <DefineConstants>$(DefineConstants);NET46</DefineConstants>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(TargetGroup)' == 'netfx'">
+    <DefineConstants>$(DefineConstants);NETFX</DefineConstants>
+  </PropertyGroup>
   <!-- Default configurations to help VS understand the configurations -->
   <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'net45-Windows_NT-Debug|AnyCPU'" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'net45-Windows_NT-Release|AnyCPU'" />
@@ -58,6 +64,9 @@
   <ItemGroup Condition=" '$(TargetGroup)' == 'netcoreapp' OR '$(TargetGroup)' == 'netstandard' OR '$(TargetGroup)' == 'net45' OR '$(TargetGroup)' == 'net46' OR '$(TargetGroup)' == 'netfx'">
     <Compile Include="System\Diagnostics\Activity.Id.MachineName.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetGroup)' == 'net46' OR '$(TargetGroup)' == 'netfx'">
+    <Compile Include="System\Diagnostics\HttpHandlerDiagnosticListener.cs" />
+  </ItemGroup>
   <ItemGroup Condition="'$(TargetGroup)' != 'net46' AND '$(TargetGroup)' != 'netfx'">
     <Reference Include="System.Collections" />
     <Reference Include="System.Diagnostics.Debug" />

src/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticListener.cs

@@ -42,6 +42,10 @@ public static IObservable<DiagnosticListener> AllListeners
         {
             get
             {
+#if NET46 || NETFX
+                GC.KeepAlive(HttpHandlerDiagnosticListener.s_instance);
+#endif
+
                 if (s_allListenerObservable == null)
                 {
                     s_allListenerObservable = new AllListenerObservable();
@@ -91,7 +95,7 @@ public virtual IDisposable Subscribe(IObserver<KeyValuePair<string, object>> obs
         /// <summary>
         /// Same as other Subscribe overload where the predicate is assumed to always return true.  
         /// </summary>
-        public IDisposable Subscribe(IObserver<KeyValuePair<string, object>> observer)
+        public virtual IDisposable Subscribe(IObserver<KeyValuePair<string, object>> observer)
         {
             return SubscribeInternal(observer, null, null);
         }