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..51b1ed134e5e2d54b346a27dba50731ebd74cff1 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)

[dcheng, 2016/12/19 11:07:40]

I think this might exclude clang-cl too? Should I add a && !defined(__clang__)
to this?

[brucedawson, 2016/12/19 19:16:00]

Easy enough to test with is_clang = true. There's also a one-time script you
have to run to enable the first download of clang (tools\clang\scripts\update.py
?)

[dcheng, 2016/12/19 20:18:11]

yeah I have a clang build setup, but I couldn't remote in.
I've checked now that I'm at my desktop. I think checks against
defined(__clang__) are usually discouraged though... thakis@, does this seem OK
to you? Or would you prefer we lose this check altogether?

Also, is there a good way to search connect to see if this issue is fixed
somewhere upstream? It'd be good to clean this is up if it becomes unnecessary
at some point in the future.

+  // 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<