Optimize conditional branches that have same true/false targets.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
===================================================================
--- runtime/vm/compiler.cc	(revision 35649)
+++ runtime/vm/compiler.cc	(working copy)
@@ -466,7 +466,8 @@
 
         if (FLAG_constant_propagation) {
           // Constant propagation can use information from range analysis to
-          // find unreachable branch targets.
+          // find unreachable branch targets and eliminate branches that have
+          // the same true- and false-target.
           ConstantPropagator::OptimizeBranches(flow_graph);
           DEBUG_ASSERT(flow_graph->VerifyUseLists());
         }