Add ExceptionPorts and its test

util/mach/exc_client_variants_test.cc

Index: util/mach/exc_client_variants_test.cc
diff --git a/util/mach/exc_client_variants_test.cc b/util/mach/exc_client_variants_test.cc
index c8692ab9bfb10c8a5ae1d82cc8876315ba6d77ae..3f2926904f67f101e3afb12434c0896526c84f56 100644
--- a/util/mach/exc_client_variants_test.cc
+++ b/util/mach/exc_client_variants_test.cc
@@ -87,8 +87,16 @@ class TestExcClientVariants : public UniversalMachExcServer,
 
     EXPECT_EQ(exception_, exception);
     EXPECT_EQ(2u, code_count);
-    EXPECT_EQ(expect_code, code[0]);
-    EXPECT_EQ(expect_subcode, code[1]);
+
+    // The code_count check above would ideally use ASSERT_EQ so that the next
+    // conditionals would not be necessary, but ASSERT_* requires a function
+    // returning type void, and the interface dictates otherwise here.
+    if (code_count >= 1) {
+      EXPECT_EQ(expect_code, code[0]);
+    }
+    if (code_count >= 2) {
+      EXPECT_EQ(expect_subcode, code[1]);
+    }
 
     if (HasState()) {
       EXPECT_EQ(exception_ + 10, *flavor);