Add type propagation phase in optimizing compiler (work in progress).

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
===================================================================
--- runtime/vm/compiler.cc	(revision 10124)
+++ runtime/vm/compiler.cc	(working copy)
@@ -173,6 +173,10 @@
         FlowGraphOptimizer optimizer(block_order);
         optimizer.ApplyICData();
 
+        // Propagate types and eliminate more type tests.
+        FlowGraphTypePropagator propagator(parsed_function, block_order);
+        propagator.PropagateTypes();
+
         if (use_ssa) {
           // Perform register allocation on the SSA graph.
           FlowGraphAllocator allocator(block_order, &graph_builder);