Complete unrolling of loops with small body and trip count one.

Rationale:
Avoids the unnecessary loop control overhead, suspend check,
and exposes more opportunities for constant folding in the
resulting loop body. Fully unrolls loop in execute() of
the Dhrystone benchmark (3% to 8% improvements).

Test: test-art-host

Change-Id: If30f38caea9e9f87a929df041dfb7ed1c227aba3
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index ea9a94c..bf13702 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -1097,6 +1097,9 @@
   // with a control flow instruction).
   void ReplaceWith(HBasicBlock* other);
 
+  // Merges the instructions of `other` at the end of `this`.
+  void MergeInstructionsWith(HBasicBlock* other);
+
   // Merge `other` at the end of `this`. This method updates loops, reverse post
   // order, links to predecessors, successors, dominators and deletes the block
   // from the graph. The two blocks must be successive, i.e. `this` the only