Build and use stack maps in the SSA compiler.

runtime/vm/locations.cc

Index: runtime/vm/locations.cc
diff --git a/runtime/vm/locations.cc b/runtime/vm/locations.cc
index 9e74025aa264727882ae28bf4648dd9febc7965d..b4a097445cf6d207db9bb4cc0a4ce98f66c640e6 100644
--- a/runtime/vm/locations.cc
+++ b/runtime/vm/locations.cc
@@ -16,7 +16,9 @@ LocationSummary::LocationSummary(intptr_t input_count,
     : input_locations_(input_count),
       temp_locations_(temp_count),
       output_location_(),
-      is_call_(contains_call == LocationSummary::kCall) {
+      stack_bitmap_(NULL),
+      is_call_(contains_call == kCall) {
+  if (is_call()) stack_bitmap_ = new BitmapBuilder();
   for (intptr_t i = 0; i < input_count; i++) {
     input_locations_.Add(Location());
   }