Pass path to platform kernel binary to kernel-service.

runtime/vm/unit_test.cc

Index: runtime/vm/unit_test.cc
diff --git a/runtime/vm/unit_test.cc b/runtime/vm/unit_test.cc
index 179e53762c10c5c5551a77b7c4c799bb34c16f91..3228eb6e2f6df435e6b7435583286e7477466a49 100644
--- a/runtime/vm/unit_test.cc
+++ b/runtime/vm/unit_test.cc
@@ -191,7 +191,8 @@ char* TestCase::CompileTestScriptWithDFE(const char* url,
                                          bool incrementally) {
   Zone* zone = Thread::Current()->zone();
   Dart_KernelCompilationResult compilation_result = Dart_CompileSourcesToKernel(
-      url, sourcefiles_count, sourcefiles, incrementally);
+      url, NULL /* platform_binary */, sourcefiles_count, sourcefiles,

[siva, 2017/08/17 15:40:57]

Why is platform_binary null here, is it because the unit tests do not depend on
anything in the platform?

I am wondering if we are testing in a different mode than what is used in
regular runs.

[aam, 2017/08/17 16:29:58]

Basically for these tests we don't have to pass path to platform.dill because it
can be found in standard place, deduced by kernel-service relative to the
executable($PATH/run_vm_tests -> $PATH/patched_sdk/platform.dill).
It felt like making this test framework aware of platform.dill was not necessary
at this point.

[siva, 2017/08/18 00:40:45]

Sounds good. I agree not necessary for the unit test framework.

+      incrementally);
 
   if (compilation_result.status != Dart_KernelCompilationStatus_Ok) {
     return OS::SCreate(zone, "Compilation failed %s", compilation_result.error);