Require explicit decorator on one arg constructors

We essentially follow this rule already, not relying on implicit
operators, although there are a number of cases where in theory we
could've implicitly constructed an object.

This commit enables the clang-tidy check.

Tested: Code compiles, passes clang-tidy.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Ia428463313b075c69614fdb326e8c5c094e7adde
diff --git a/.clang-tidy b/.clang-tidy
index d892bdd..bed3fad 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -222,6 +222,7 @@
 cppcoreguidelines-pro-type-vararg,
 cppcoreguidelines-slicing,
 cppcoreguidelines-special-member-functions,
+google-explicit-constructor,
 misc-misplaced-const,
 #misc-no-recursion,
 misc-redundant-expression,