Add ExceptionPorts and its test

util/mach/exc_server_variants_test.cc

Index: util/mach/exc_server_variants_test.cc
diff --git a/util/mach/exc_server_variants_test.cc b/util/mach/exc_server_variants_test.cc
index 6800b4382c9152209db2972be551fae27c5253f1..c43b5621f2ef57f1b7410e89d97ce046bfbf9ee6 100644
--- a/util/mach/exc_server_variants_test.cc
+++ b/util/mach/exc_server_variants_test.cc
@@ -909,7 +909,10 @@ class TestExcServerVariants : public UniversalMachExcServer,
     EXPECT_EQ(EXC_CRASH, exception);
     EXPECT_EQ(2u, code_count);
 
-    if (code_count > 1) {
+    // The code_count check above would ideally use ASSERT_EQ so that the next
+    // conditional would not be necessary, but ASSERT_* requires a function
+    // returning type void, and the interface dictates otherwise here.
+    if (code_count >= 1) {
       // The signal that terminated the process is stored in code[0] along with
       // some other data. See 10.9.4 xnu-2422.110.17/bsd/kern/kern_exit.c
       // proc_prepareexit().