Improve the graph visualizer's output for constant locations.

Change-Id: I423fb378ee61fb53c3b328fc74f4e95cdef0992a
diff --git a/compiler/optimizing/graph_visualizer.cc b/compiler/optimizing/graph_visualizer.cc
index 0b4c569..89d80cc 100644
--- a/compiler/optimizing/graph_visualizer.cc
+++ b/compiler/optimizing/graph_visualizer.cc
@@ -298,6 +298,12 @@
         stream << constant->AsIntConstant()->GetValue();
       } else if (constant->IsLongConstant()) {
         stream << constant->AsLongConstant()->GetValue();
+      } else if (constant->IsFloatConstant()) {
+        stream << constant->AsFloatConstant()->GetValue();
+      } else if (constant->IsDoubleConstant()) {
+        stream << constant->AsDoubleConstant()->GetValue();
+      } else if (constant->IsNullConstant()) {
+        stream << "null";
       }
     } else if (location.IsInvalid()) {
       stream << "invalid";