WIP: Code coverage with gcov

ios/showcase/test/showcase_test_case.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/showcase/test/showcase_test_case.h"
 
 #import <EarlGrey/EarlGrey.h>
 
 #import "base/logging.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #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
 // necessary.
 + (NSArray*)testInvocations {
   NSError* error = nil;
   [[EarlGrey selectElementWithMatcher:grey_systemAlertViewShown()]
       assertWithMatcher:grey_nil()
                   error:&error];
   if (error != nil) {
     LOG(ERROR) << "System alert view is present, so skipping all tests.";
     return @[];
   }
   return [super testInvocations];
 }
 
++ (void)tearDown {
+  __gcov_flush();
+}
+
 @end