Bump to mono/mono/2019-10@c0c5c7 (#4286)

Context: https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1070776/
Context: mono/mono#18764
Context: mono/mono#18832

Changes: mono/mono@1cca0cf...c0c5c78

  * mono/mono@c0c5c78e2bd: Bump bockbuild to bring in Gtk# regression fix (#18912)
  * mono/mono@a644983ae82: [2019-10] Make MonoWebRequestHandler linker friendly (#18835)
  * mono/mono@85f47fae28e: Move HttpClientHandlerTests.Android.cs to nunit (#18888)
  * mono/mono@26afa2d5bb7: [2019-10] Bump msbuild to track mono-2019-10 (#18861)
  * mono/mono@e5f0d5d928a: [2019-10] [merp] Increase buffer size for state dump (#18838)
  * mono/mono@e60eabc7670: Move offsets-tool into mono/tools (#18783) (#18831)
  * mono/mono@7a59bf3ea51: [2019-10] Bump msbuild to track mono-2019-10 (#18791)
  * mono/mono@47bb780c8d7: [2019-10] Allow users to switch to MonoWebRequestHandler on Android via UI (#18787)
  * mono/mono@d6f592717e1: Bump bockbuild to get GTK NSPasteboardType change.
  * mono/mono@1ee12f86258: Update deprecated query parameter to header (#18705)
  * mono/mono@87201428343: [iOS] Replace removed dsymutil `-t` switch with `-num-threads` (#18743)
  * mono/mono@83c161f2766: Skip WebAssembly build in sdks archive build on non-master branches
  * mono/mono@0e18125d711: [merp] Add an exception type for managed exceptions (#18722)
  * mono/mono@82fffe07497: [runtime] Disable lldb backtrace display on osx, it hangs on attaching in lldb.

d16-4 broke NTLM Authentication with `HttpClient` in Xamarin.Android.

To now use NTLM Authentication, the `$(AndroidHttpClientHandlerType)`
MSBuild variable must be overridden from the default value:

	<PropertyGroup>
	  <AndroidHttpClientHandlerType>System.Net.Http.MonoWebRequestHandler, System.Net.Http</AndroidHttpClientHandlerType>
	</PropertyGroup>

See mono/mono#18764 for more details.

.external

@@ -1,2 +1,2 @@
 xamarin/monodroid:d16-5@dab75e88055c1bfaf53f810b0c3a9218fc53c60a
-mono/mono:2019-10@1cca0cfebfcbd019c6f2bdd3e5b99f769f1e2e0c
+mono/mono:2019-10@c0c5c78e2bdbdbf7a70ae10b0a698708f1f2edbe

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/LinkerTests.cs

@@ -87,23 +87,31 @@ static AssemblyDefinition CreateFauxMonoAndroidAssembly ()
 			return assm;
 		}
 
-		[Test]
-		public void PreserveAndroidHttpClientHandler ()
+		private void PreserveCustomHttpClientHandler (string handlerType, string handlerAssembly, string testProjectName, string assemblyPath)
 		{
-			var handlerType = "Xamarin.Android.Net.AndroidClientHandler";
 			var proj = new XamarinAndroidApplicationProject () { IsRelease = true };
 			proj.AddReferences ("System.Net.Http");
-			proj.SetProperty (proj.ActiveConfigurationProperties, "AndroidHttpClientHandlerType", handlerType);
+			string handlerTypeFullName = string.IsNullOrEmpty(handlerAssembly) ? handlerType : handlerType + ", " + handlerAssembly;
+			proj.SetProperty (proj.ActiveConfigurationProperties, "AndroidHttpClientHandlerType", handlerTypeFullName);
 			proj.MainActivity = proj.DefaultMainActivity.Replace ("base.OnCreate (bundle);", "base.OnCreate (bundle);\nvar client = new System.Net.Http.HttpClient ();");
-			using (var b = CreateApkBuilder ("temp/PreserveAndroidHttpClientHandler")) {
+			using (var b = CreateApkBuilder (testProjectName)) {
 				Assert.IsTrue (b.Build (proj), "Build should have succeeded.");
 
-				using (var assembly = AssemblyDefinition.ReadAssembly (Path.Combine (Root, b.ProjectDirectory, proj.IntermediateOutputPath, "android/assets/Mono.Android.dll"))) {
-					Assert.IsTrue (assembly.MainModule.GetType (handlerType) != null, "Xamarin.Android.Net.AndroidClientHandler should have been preserved by the linker.");
+				using (var assembly = AssemblyDefinition.ReadAssembly (Path.Combine (Root, b.ProjectDirectory, proj.IntermediateOutputPath, assemblyPath))) {
+					Assert.IsTrue (assembly.MainModule.GetType (handlerType) != null, $"'{handlerTypeFullName}' should have been preserved by the linker.");
 				}
 			}
 		}
 
+		[Test]
+		public void PreserveCustomHttpClientHandlers ()
+		{
+			PreserveCustomHttpClientHandler ("Xamarin.Android.Net.AndroidClientHandler", "",
+				"temp/PreserveAndroidHttpClientHandler", "android/assets/Mono.Android.dll");
+			PreserveCustomHttpClientHandler ("System.Net.Http.MonoWebRequestHandler", "System.Net.Http",
+				"temp/PreserveMonoWebRequestHandler", "android/assets/System.Net.Http.dll");
+		}
+
 		[Test]
 		public void WarnAboutAppDomainsRelease ()
 		{

tests/BCL-Tests/Xamarin.Android.Bcl-Tests/nunit-excluded-tests.txt

@@ -35,3 +35,6 @@ MonoTests.System.Web.Services.Description.ServiceDescriptionTest.ReadAndRetrieva
 MonoTests.System.Web.Services.Description.ServiceDescriptionTest.ReadInvalid
 MonoTests.System.Web.Services.Description.ServiceDescriptionTest.SimpleWrite
 MonoTests.System.Web.Services.Description.ServiceDescriptionTest.ValidatingRead
+
+# the test is incorrect and will be removed soon: https://github.com/mono/mono/pull/18952
+System.Net.Http.Tests.HttpClientHandlerTestsAndroid.TestEnvVarSwitchForInnerHttpHandler