Add a compilation tracing mechanism to the new compiler.

Code mostly imported from: https://android-review.googlesource.com/#/c/81653/.

Change-Id: I150fe942be0fb270e03fabb19032180f7a065d13
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index bbebd3a..beafbcc 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -47,7 +47,7 @@
   Bind(GetLabelOf(block));
   HGraphVisitor* location_builder = GetLocationBuilder();
   HGraphVisitor* instruction_visitor = GetInstructionVisitor();
-  for (HInstructionIterator it(*block->GetInstructions()); !it.Done(); it.Advance()) {
+  for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
     HInstruction* current = it.Current();
     current->Accept(location_builder);
     InitLocations(current);