Implement basic support for deferred slow path code with calls that save and restore live registers.

runtime/vm/locations.cc

Index: runtime/vm/locations.cc
diff --git a/runtime/vm/locations.cc b/runtime/vm/locations.cc
index b4a097445cf6d207db9bb4cc0a4ce98f66c640e6..92385d600736d7f2f96026caa176fc42c0039b2f 100644
--- a/runtime/vm/locations.cc
+++ b/runtime/vm/locations.cc
@@ -17,14 +17,18 @@ LocationSummary::LocationSummary(intptr_t input_count,
       temp_locations_(temp_count),
       output_location_(),
       stack_bitmap_(NULL),
-      is_call_(contains_call == kCall) {
-  if (is_call()) stack_bitmap_ = new BitmapBuilder();
+      contains_call_(contains_call),
+      live_registers_() {
   for (intptr_t i = 0; i < input_count; i++) {
     input_locations_.Add(Location());
   }
   for (intptr_t i = 0; i < temp_count; i++) {
     temp_locations_.Add(Location());
   }
+
+  if (contains_call_ != kNoCall) {
+    stack_bitmap_ = new BitmapBuilder();
+  }
 }