Explicitly delete some Callback constructors to improve errors.

base/bind_unittest.cc

Index: base/bind_unittest.cc
diff --git a/base/bind_unittest.cc b/base/bind_unittest.cc
index c6b53d55f031e557e3bf7886a7512a09d816a43d..5892c7485dbbfda2ca03c999fd6996f956473a18 100644
--- a/base/bind_unittest.cc
+++ b/base/bind_unittest.cc
@@ -1316,6 +1316,9 @@ TEST_F(BindTest, OnceCallback) {
       "RepeatingClosure should be move-assignable");
 
   // Conversions from OnceCallback to RepeatingCallback.
+#if !defined(COMPILER_MSVC) || defined(__clang__)
+  // In theory, this should have been fixed in VS2015 update 2:
+  // https://connect.microsoft.com/VisualStudio/feedback/details/819202
   static_assert(!std::is_constructible<
       RepeatingClosure, const OnceClosure&>::value,
       "OnceClosure should not be convertible to RepeatingClosure.");
@@ -1330,6 +1333,7 @@ TEST_F(BindTest, OnceCallback) {
   static_assert(!is_assignable<
       RepeatingClosure, OnceClosure&&>::value,
       "OnceClosure should not be convertible to RepeatingClosure.");
+#endif
 
   // Copy constructor and assignment of OnceCallback.
   static_assert(!std::is_constructible<