Add tools for code coverage support in iOS.

build/config/ios/BUILD.gn

 # 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("//build/config/ios/ios_sdk.gni")
 import("//build/config/sysroot.gni")
 import("//build/toolchain/toolchain.gni")
 
 declare_args() {
   # Enabling this option makes clang compile to an intermediate
@@ skipping 94 matching lines @@
   if (use_xcode_clang && get_path_info(ios_sdk_version, "name") != "10") {
     common_cc_flags = [
       "-isystem",
       rebase_path("//third_party/llvm-build/Release+Asserts/include/c++/v1",
                   root_build_dir),
     ]
 
     cflags_cc = common_cc_flags
     cflags_objcc = common_cc_flags
   }
+
+  if (ios_enable_coverage) {
+    configs = [ ":enable_coverage" ]
+  }
 }
 
 config("ios_executable_flags") {
 }
 
 config("ios_dynamic_flags") {
   ldflags = [ "-Wl,-ObjC" ]  # Always load Objective-C categories and class.
 }
 
 config("xctest_config") {
   common_flags = [
     "-F",
     "$ios_sdk_platform_path/Developer/Library/Frameworks",
   ]
 
   cflags = common_flags
   ldflags = common_flags
 
   libs = [
     "Foundation.framework",
     "XCTest.framework",
   ]
 }
 
+# This enables support for LLVM code coverage. See
+# http://llvm.org/docs/CoverageMappingFormat.html.
+config("enable_coverage") {
+  cflags = [
+    "-fprofile-instr-generate",
+    "-fcoverage-mapping",
+  ]
+  ldflags = [ "-fprofile-instr-generate" ]
+}
+
 group("xctest") {
   public_configs = [ ":xctest_config" ]
 }