dbus: Add missing destructors to Property and PropertyBase.

BUG=none

Review URL: https://codereview.chromium.org/1237343003

Cr-Commit-Position: refs/heads/master@{#339031}
diff --git a/dbus/property.cc b/dbus/property.cc
index 66b86c0..dde0611 100644
--- a/dbus/property.cc
+++ b/dbus/property.cc
@@ -18,6 +18,10 @@
 // PropertyBase implementation.
 //
 
+PropertyBase::PropertyBase() : property_set_(nullptr), is_valid_(false) {}
+
+PropertyBase::~PropertyBase() {}
+
 void PropertyBase::Init(PropertySet* property_set, const std::string& name) {
   DCHECK(!property_set_);
   property_set_ = property_set;