Add nonstd::unique_ptr move assigment operator.

third_party/base/nonstd_unique_ptr.h

Index: third_party/base/nonstd_unique_ptr.h
diff --git a/third_party/base/nonstd_unique_ptr.h b/third_party/base/nonstd_unique_ptr.h
index 1d1c43f42fb4ac706cb1ce01795b03f986e6c58a..96ea19a55d4caebcf3f7ad5b4d5ad19f4d40a895 100644
--- a/third_party/base/nonstd_unique_ptr.h
+++ b/third_party/base/nonstd_unique_ptr.h
@@ -176,6 +176,18 @@ class unique_ptr : public unique_ptr_base<C> {
     }
   }
 
+  // Move assignment.
+  unique_ptr<C>& operator=(unique_ptr<C>&& that) {
+    if (that.ptr_ != ptr_) {

[Jeffrey Yasskin, 2015/09/22 20:12:55]

Implement this as "reset(that.release());"

[Tom Sepez, 2015/09/22 22:05:13]

Done. clever.

+      enum { type_must_be_complete = sizeof(C) };
+      C* old_ptr = ptr_;
+      ptr_ = that.ptr_;
+      that.ptr_ = nullptr;
+      delete old_ptr;
+    }
+    return *this;
+  }
+
 private:
   // Forbid comparison of unique_ptr types.  If C2 != C, it totally doesn't
   // make sense, and if C2 == C, it still doesn't make sense because you should