Run DCE again after all the other optimizations have run.

On docs this doubles the amount of instructions removed.
diff --git a/compiler/optimizing/dead_code_elimination.cc b/compiler/optimizing/dead_code_elimination.cc
index 9499040..8045cc5 100644
--- a/compiler/optimizing/dead_code_elimination.cc
+++ b/compiler/optimizing/dead_code_elimination.cc
@@ -41,6 +41,7 @@
           && !inst->IsMemoryBarrier()  // If we added an explicit barrier then we should keep it.
           && !inst->HasUses()) {
         block->RemoveInstruction(inst);
+        MaybeRecordStat(MethodCompilationStat::kRemovedDeadInstruction);
       }
     }
   }