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/compilers.h b/compiler/compilers.h
index 3ca78c9..e523d64 100644
--- a/compiler/compilers.h
+++ b/compiler/compilers.h
@@ -73,7 +73,7 @@
 
 class OptimizingCompiler FINAL : public QuickCompiler {
  public:
-  explicit OptimizingCompiler(CompilerDriver* driver) : QuickCompiler(driver) { }
+  explicit OptimizingCompiler(CompilerDriver* driver);
 
   CompiledMethod* Compile(const DexFile::CodeItem* code_item,
                           uint32_t access_flags,
@@ -92,6 +92,8 @@
                              const DexFile& dex_file) const;
 
  private:
+  UniquePtr<std::ostream> visualizer_output_;
+
   DISALLOW_COPY_AND_ASSIGN(OptimizingCompiler);
 };