WIP: Code coverage with gcov

ios/showcase/test/showcase_test_case.mm

Index: ios/showcase/test/showcase_test_case.mm
diff --git a/ios/showcase/test/showcase_test_case.mm b/ios/showcase/test/showcase_test_case.mm
index e4877f11f752c2f49acdf50c1365ed9b58d52c2a..43f694e67bdc0d014923f76cbfd50d176620edb1 100644
--- a/ios/showcase/test/showcase_test_case.mm
+++ b/ios/showcase/test/showcase_test_case.mm
@@ -12,6 +12,8 @@
 #error "This file requires ARC support."
 #endif
 
+extern "C" void __gcov_flush(void);
+
 @implementation ShowcaseTestCase
 
 // Overrides testInvocations so the set of tests run can be modified, as
@@ -28,4 +30,8 @@
   return [super testInvocations];
 }
 
++ (void)tearDown {
+  __gcov_flush();
+}
+
 @end