Add support for computing iOS code coverage

Also disable failing PosixSignalDeliveryTest* tests for iOS

Bug: chromium:844647
Change-Id: I64bb233bef2f06f6778f2d475b6d3ad685fb9143
Reviewed-on: https://webrtc-review.googlesource.com/c/105641
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Peter Hanspers <peterhanspers@webrtc.org>
Reviewed-by: Artem Titarenko <artit@webrtc.org>
Commit-Queue: Artem Titarenko <artit@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25524}

test/ios/coverage_util_ios.h

@@ -0,0 +1,24 @@
+/*
+ *  Copyright 2018 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef TEST_IOS_COVERAGE_UTIL_IOS_H_
+#define TEST_IOS_COVERAGE_UTIL_IOS_H_
+
+namespace rtc {
+namespace test {
+
+// In debug builds, if IOS_ENABLE_COVERAGE is defined, sets the filename of the
+// coverage file. Otherwise, it does nothing.
+void ConfigureCoverageReportPath();
+
+}  // namespace test
+}  // namespace rtc
+
+#endif  // TEST_IOS_COVERAGE_UTIL_IOS_H_