Add functionality to find xctest files under application target.

tools/gn/xcode_writer.h

Index: tools/gn/xcode_writer.h
diff --git a/tools/gn/xcode_writer.h b/tools/gn/xcode_writer.h
index 87a7d589c11380b006fe4bf6a0849925aedad2eb..cbe3341ef86cba68f38f5a29f90beae18b8e30c9 100644
--- a/tools/gn/xcode_writer.h
+++ b/tools/gn/xcode_writer.h
@@ -64,6 +64,13 @@ class XcodeWriter {
                             std::vector<const Target*>* targets,
                             Err* err);
 
+  // Filters the list of targets to only return xctest targets and their
+  // corresonding application targets.

[sdefresne, 2016/12/14 13:00:03]

nit: corresonding -> corresponding

[liaoyuke, 2016/12/15 00:03:12]

Done.

+  static void FilterXCTestTargets(
+      const std::vector<const Target*>& targets,
+      std::vector<const Target*>* xctest_targets,
+      std::vector<const Target*>* application_targets);
+
   // Generate the "products.xcodeproj" project that reference all products
   // (i.e. targets that have a build artefact usable from Xcode, mostly
   // application bundles).