Add missing references.

This mainly avoids implicit copies when extracting an object from a container.

Change-Id: If4d0e6153e8c2b48345fde5bb546b4c65649fcf3
diff --git a/compiler/dex/ssa_transformation.cc b/compiler/dex/ssa_transformation.cc
index 366d7f2..0ca5fd4 100644
--- a/compiler/dex/ssa_transformation.cc
+++ b/compiler/dex/ssa_transformation.cc
@@ -179,7 +179,7 @@
   bb->visited = true;
   work_stack.push_back(std::make_pair(bb, new (arena_) ArenaBitVector::Iterator(bb->i_dominated)));
   while (!work_stack.empty()) {
-    std::pair<BasicBlock*, ArenaBitVector::Iterator*> curr = work_stack.back();
+    const std::pair<BasicBlock*, ArenaBitVector::Iterator*>& curr = work_stack.back();
     BasicBlock* curr_bb = curr.first;
     ArenaBitVector::Iterator* curr_idom_iter = curr.second;
     int bb_idx = curr_idom_iter->Next();
diff --git a/compiler/oat_writer.cc b/compiler/oat_writer.cc
index f9d6e41..f23b72b 100644
--- a/compiler/oat_writer.cc
+++ b/compiler/oat_writer.cc
@@ -667,7 +667,7 @@
   const CompiledMethod* compiled_method =
       compiler_driver_->GetCompiledMethod(MethodReference(&dex_file, method_idx));
 
-  OatMethodOffsets method_offsets =
+  const OatMethodOffsets& method_offsets =
       oat_classes_[oat_class_index]->method_offsets_[class_def_method_index];
 
 
diff --git a/runtime/stack.cc b/runtime/stack.cc
index 1715664..5d3a9a5 100644
--- a/runtime/stack.cc
+++ b/runtime/stack.cc
@@ -253,7 +253,7 @@
   return result;
 }
 
-instrumentation::InstrumentationStackFrame StackVisitor::GetInstrumentationStackFrame(uint32_t depth) const {
+instrumentation::InstrumentationStackFrame& StackVisitor::GetInstrumentationStackFrame(uint32_t depth) const {
   return thread_->GetInstrumentationStack()->at(depth);
 }
 
@@ -309,7 +309,7 @@
           // While profiling, the return pc is restored from the side stack, except when walking
           // the stack for an exception where the side stack will be unwound in VisitFrame.
           if (GetQuickInstrumentationExitPc() == return_pc) {
-            instrumentation::InstrumentationStackFrame instrumentation_frame =
+            const instrumentation::InstrumentationStackFrame& instrumentation_frame =
                 GetInstrumentationStackFrame(instrumentation_stack_depth);
             instrumentation_stack_depth++;
             if (GetMethod() == Runtime::Current()->GetCalleeSaveMethod(Runtime::kSaveAll)) {
diff --git a/runtime/stack.h b/runtime/stack.h
index 700b7f1..a4b93bc 100644
--- a/runtime/stack.h
+++ b/runtime/stack.h
@@ -567,7 +567,7 @@
   static void DescribeStack(Thread* thread) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  private:
-  instrumentation::InstrumentationStackFrame GetInstrumentationStackFrame(uint32_t depth) const;
+  instrumentation::InstrumentationStackFrame& GetInstrumentationStackFrame(uint32_t depth) const;
 
   void SanityCheckFrame() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);