Modify ALLOW_UNUSED to allow enabling unused local warnings on MSVC.

This splits the macro into two:

int a = 1;
ALLOW_UNUSED_LOCAL(a);

and

typedef Foo Bar ALLOW_UNUSED_TYPE;
void foo() ALLOW_UNUSED_TYPE;  // ALLOW_UNUSED_TYPE_OR_FUNC seemed too verbose

This matches changes that have already been made in Blink.

BUG=81439
TEST=none
TBR=ben

Review URL: https://codereview.chromium.org/650393002

Cr-Commit-Position: refs/heads/master@{#300014}


CrOS-Libchrome-Original-Commit: 99867ef78bf14ad37e263860248d0a2d61b51a73
diff --git a/base/tuple_unittest.cc b/base/tuple_unittest.cc
index 402394c..8d620de 100644
--- a/base/tuple_unittest.cc
+++ b/base/tuple_unittest.cc
@@ -30,7 +30,8 @@
 }  // namespace
 
 TEST(TupleTest, Basic) {
-  Tuple0 t0 ALLOW_UNUSED = MakeTuple();
+  Tuple0 t0 = MakeTuple();
+  ALLOW_UNUSED_LOCAL(t0);
   Tuple1<int> t1(1);
   Tuple2<int, const char*> t2 = MakeTuple(1, static_cast<const char*>("wee"));
   Tuple3<int, int, int> t3(1, 2, 3);