Fixing remaining VC++ 2015 64-bit build breaks

sandbox/win/src/handle_inheritance_test.cc

Index: sandbox/win/src/handle_inheritance_test.cc
diff --git a/sandbox/win/src/handle_inheritance_test.cc b/sandbox/win/src/handle_inheritance_test.cc
index 1a411b543b41388c7b5698b968f0583bf72b3322..4fb98f1c8bb07aac490d7f25bbf945302c1f8cd8 100644
--- a/sandbox/win/src/handle_inheritance_test.cc
+++ b/sandbox/win/src/handle_inheritance_test.cc
@@ -82,9 +82,12 @@ TEST(HandleInheritanceTests, InheritByValue) {
   void* shared_handle = runner.GetPolicy()->AddHandleToShare(
       test_shared_memory.handle().GetHandle());
 
-  std::string command_line =
-      "HandleInheritanceTests_ValidInheritedHandle " +
-      base::UintToString(reinterpret_cast<unsigned int>(shared_handle));
+  std::string command_line = "HandleInheritanceTests_ValidInheritedHandle " +
+                             // Cast through uintptr_t and then unsigned int to
+                             // make the truncation explicit. Handles are size
+                             // of-pointer but are always 32-bit values.
+                             base::UintToString(static_cast<unsigned int>(
+                                 reinterpret_cast<uintptr_t>(shared_handle)));
   int result = runner.RunTest(base::UTF8ToUTF16(command_line).c_str());
   ASSERT_EQ(SBOX_TEST_SUCCEEDED, result);
 }