Get size using --get-size in flashrom_util.py instead of reading whole flash.

client/site_tests/firmware_RomSize/firmware_RomSize.py

Index: client/site_tests/firmware_RomSize/firmware_RomSize.py
diff --git a/client/site_tests/firmware_RomSize/firmware_RomSize.py b/client/site_tests/firmware_RomSize/firmware_RomSize.py
index 3efab28b8c2906d9a8969ebf92d8245a4617e110..9bccda7da36d7dc702fde929cdb2d23d97608a8f 100644
--- a/client/site_tests/firmware_RomSize/firmware_RomSize.py
+++ b/client/site_tests/firmware_RomSize/firmware_RomSize.py
@@ -7,7 +7,7 @@ from autotest_lib.client.common_lib import error
 from autotest_lib.client.common_lib import flashrom_util
 
 class firmware_RomSize(test.test):
-    version = 2
+    version = 3
 
     def run_once(self):
         flashrom = flashrom_util.flashrom_util()
@@ -18,5 +18,8 @@ class firmware_RomSize(test.test):
         flashrom.select_ec_flashrom()
         ec_size = flashrom.get_size() / 1024
 
+        # Always restore system flashrom selection to BIOS.
+        flashrom.select_bios_flashrom()
+
         self.write_perf_keyval({"kb_system_rom_size": bios_size,
                                 "kb_ec_rom_size": ec_size})