Use size_t in SetupUtilTest.GetToastActivatorRegistryPath

Change-Id: Ice85ebdd73350f8228a7591496716d73efe3695b
Reviewed-on: https://chromium-review.googlesource.com/922862
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537265}

chrome/installer/setup/setup_util_unittest.cc

@@ -465,7 +465,7 @@ TEST(SetupUtilTest, GetToastActivatorRegistryPath) {
   EXPECT_EQ(L'\\', toast_activator_reg_path[guid_begin - 1]);
 
   // A GUID has the form "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}".
-  constexpr unsigned int kGuidLength = 38;
+  constexpr size_t kGuidLength = 38;
   EXPECT_EQ(kGuidLength, toast_activator_reg_path.length() - guid_begin);
 
   EXPECT_EQ('}', toast_activator_reg_path.back());