Add ability to check /etc/lsb-release for HWID

This is enabled by a compile-time option, only.

On certain boards HWID may not be available via normal means.
This functionality allows a compile-time choice to enable
behavior that will check /etc/lsb-release for an
HWID_OVERRIDE=<id> entry instead.

CQ-DEPEND=CL:186482
BUG=None
TEST=unit tests

Change-Id: I1279ea142a3b08dc4c50c527d8ee8f7b44c4a63f
Reviewed-on: https://chromium-review.googlesource.com/186483
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Chris Masone <cmasone@chromium.org>
diff --git a/hardware.h b/hardware.h
index 2693e3b..8168d9c 100644
--- a/hardware.h
+++ b/hardware.h
@@ -14,7 +14,8 @@
 // Implements the real interface with the hardware.
 class Hardware : public HardwareInterface {
  public:
-  Hardware() {}
+  Hardware();
+  virtual ~Hardware();
 
   // HardwareInterface methods.
   virtual const std::string BootKernelDevice();