Fix shill unittest build problem for gcc 4.7.

gcc 4.7 is more strict about type conversion in initilization list,
for example -

const char apple[] = {0xff, 0xfe};

The above compiles ok prior to gcc 4.7, but fails on gcc 4.7 with
-Wall -Werror. The reason is that 0xff is out of bound for (signed)
char type.

TEST=Built/tested using gcc 4.7
BUG=None

Change-Id: I597cac783954b856726494b757d69ddbc6c4436b
Reviewed-on: https://gerrit.chromium.org/gerrit/31908
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Han Shen <shenhan@chromium.org>
Tested-by: Han Shen <shenhan@chromium.org>
diff --git a/property_store_unittest.cc b/property_store_unittest.cc
index 2256ff3..79239d0 100644
--- a/property_store_unittest.cc
+++ b/property_store_unittest.cc
@@ -123,7 +123,8 @@
   PropertyStore store;
   Error error;
   TypeParam property;
-  RegisterProperty(store, "some property", &property);
+  // |this| required due to two-phase lookup.
+  this->RegisterProperty(store, "some property", &property);
   EXPECT_TRUE(store.ClearProperty("some property", &error));
 }