Add tools for code coverage support in iOS.

testing/coverage_util_ios.mm

+// Copyright 2014 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 <Foundation/Foundation.h>
+
+extern "C" void __llvm_profile_set_filename(const char* name);
+
+namespace coverage_util {
+
+void SetupIfNecessary() {
+#if !defined(NDEBUG)  // && defined(ENABLE_TEST_CODE_COVERAGE)

[baxley, 2017/04/03 17:18:53]

nit: do we want the commented out condition?

+  static dispatch_once_t once_token;
+  dispatch_once(&once_token, ^{
+    // Writes the profraw file to the Documents directory, where the app has
+    // write rights.
+    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
+                                                         NSUserDomainMask, YES);
+    NSString* documents_directory = [paths firstObject];
+    NSString* file_name = [documents_directory
+        stringByAppendingPathComponent:@"coverage.profraw"];
+
+    // For documentation, see:
+    // http://clang.llvm.org/docs/SourceBasedCodeCoverage.html
+    __llvm_profile_set_filename([file_name UTF8String]);
+
+    // Print the path for easier retrieval.
+    NSLog(@"Coverage data at %@.", file_name);
+  });
+#endif
+}
+
+}  // namespace coverage_util