Fixed races in EventCounters. Preped to add Dispose() method

There were a number of races in EventCounters.  Did an audit and fixed these.
Also prepped to add a  Dispose() method so that you can make counters for transient objects (e.g. files)
Have actually made it public yet, pending API review.
Also turned on and beefed up the testing.  Fixed tests.

src/System.Diagnostics.DiagnosticSource/System.Diagnostics.DiagnosticSource.sln

@@ -1,6 +1,6 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 14
-VisualStudioVersion = 14.0.25420.1
+# Visual Studio 15
+VisualStudioVersion = 15.0.26430.12
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "System.Diagnostics.DiagnosticSource.Tests", "tests\System.Diagnostics.DiagnosticSource.Tests.csproj", "{A7922FA3-306A-41B9-B8DC-CC4DBE685A85}"
 	ProjectSection(ProjectDependencies) = postProject
@@ -20,6 +20,15 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{E107E9C1-E89
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "ref", "ref", "{2E666815-2EDB-464B-9DF6-380BF4789AD4}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{33F18BCF-3CA9-4AF8-B78A-9A9042D60092}"
+	ProjectSection(SolutionItems) = preProject
+		src\ActivityUserGuide.md = src\ActivityUserGuide.md
+		src\DiagnosticSourceUsersGuide.md = src\DiagnosticSourceUsersGuide.md
+		src\FlatRequestId.md = src\FlatRequestId.md
+		src\HierarchicalRequestId.md = src\HierarchicalRequestId.md
+		src\HttpCorrelationProtocol.md = src\HttpCorrelationProtocol.md
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU

src/System.Diagnostics.Tracing/src/System.Diagnostics.Tracing.csproj

@@ -8,7 +8,7 @@
     <!-- CSC adds a typeforward for the internal nested type EventSource.EventMetadata but
          GenFacades doesn't consider this as a viable target for a typeforward since it's internal -->
     <GenFacadesIgnoreMissingTypes Condition="'$(TargetGroup)' == 'netfx'">true</GenFacadesIgnoreMissingTypes>
-    <DefineContants Condition="'$(TargetGroup)' != 'netfx'">$(DefineConstants);SUPPORTS_EVENTCOMMANDEXECUTED</DefineContants>
+    <DefineConstants Condition="'$(TargetGroup)' == 'netfx'">$(DefineConstants);NO_EVENTCOMMANDEXECUTED_SUPPORT</DefineConstants> 
   </PropertyGroup>
   <!-- Default configurations to help VS understand the options -->
   <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'netcoreapp-Unix-Debug|AnyCPU'" />
@@ -30,6 +30,7 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetGroup)' == 'netfx'">
     <Reference Include="mscorlib" />
+    <Reference Include="System" />
   </ItemGroup>
   <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
-</Project>
+</Project>