Move IsBootDeviceRemovable() to the HardwareInterface.

The UpdateCheckScheduler class had a IsBootDeviceRemovable method to
mock out the value during testing of that class. Instead, this patch
uses the HardwareInterface to mock out that value.

BUG=chromium:358269
TEST=Unittests updated.

Change-Id: Ib20f70fa0468aaa4bc8bb1b674084bd9a61e5085
Reviewed-on: https://chromium-review.googlesource.com/197598
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
diff --git a/hardware_interface.h b/hardware_interface.h
index bc7fee3..83db8a2 100644
--- a/hardware_interface.h
+++ b/hardware_interface.h
@@ -26,6 +26,9 @@
   // Returns the currently booted rootfs partition. "/dev/sda3", for example.
   virtual std::string BootDevice() const = 0;
 
+  // Return whether the BootDevice() is a removable device.
+  virtual bool IsBootDeviceRemovable() const = 0;
+
   // Returns a list of all kernel partitions available (whether bootable or not)
   virtual std::vector<std::string> GetKernelDevices() const = 0;