ART: Change InstructionSetFeatures to return unique_ptr

This makes clear the ownership of the object.

Test: m test-art-host
Change-Id: I55fa734f04bc3046d370f4dcf98ce6b17c59e234
diff --git a/compiler/optimizing/optimizing_cfi_test.cc b/compiler/optimizing/optimizing_cfi_test.cc
index bacf994..013e110 100644
--- a/compiler/optimizing/optimizing_cfi_test.cc
+++ b/compiler/optimizing/optimizing_cfi_test.cc
@@ -52,7 +52,7 @@
   void SetUpFrame(InstructionSet isa) {
     // Setup simple context.
     std::string error;
-    isa_features_.reset(InstructionSetFeatures::FromVariant(isa, "default", &error));
+    isa_features_ = InstructionSetFeatures::FromVariant(isa, "default", &error);
     graph_ = CreateGraph(&allocator_);
     // Generate simple frame with some spills.
     code_gen_ = CodeGenerator::Create(graph_, isa, *isa_features_, opts_);