Fix a crash in graoh builder where a throw node is added in an expression tree by the parser: allow…

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
===================================================================
--- runtime/vm/flow_graph_builder.cc	(revision 6338)
+++ runtime/vm/flow_graph_builder.cc	(working copy)
@@ -1843,7 +1843,7 @@
 }
 
 
-void EffectGraphVisitor::VisitThrowNode(ThrowNode* node) {
+void EffectGraphVisitor::BuildThrowNode(ThrowNode* node) {
   ValueGraphVisitor for_exception(owner(), temp_index());
   node->exception()->Visit(&for_exception);
   Append(for_exception);
@@ -1861,10 +1861,24 @@
                              for_stack_trace.value());
   }
   AddInstruction(instr);
+}
+
+
+void EffectGraphVisitor::VisitThrowNode(ThrowNode* node) {
+  BuildThrowNode(node);
   CloseFragment();
 }
 
 
+// A throw cannot be part of an expression, however, the parser may replace
+// certain expression nodes with a throw. In that case generate a literal null
+// so that the fragment is not closed in the middle of an expression.
+void ValueGraphVisitor::VisitThrowNode(ThrowNode* node) {
+  BuildThrowNode(node);
+  ReturnValue(new ConstantVal(Instance::ZoneHandle()));
+}
+
+
 void EffectGraphVisitor::VisitInlinedFinallyNode(InlinedFinallyNode* node) {
   Bailout("EffectGraphVisitor::VisitInlinedFinallyNode");
 }