Revive throw as an expression but not for rethrow.

sdk/lib/_internal/compiler/implementation/ssa/builder.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/builder.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(revision 15894)
+++ sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(working copy)
@@ -3764,6 +3764,7 @@
   }
 
   visitThrow(Throw node) {
+    HBasicBlock block;
     if (node.expression == null) {
       HInstruction exception = rethrowableException;
       if (exception == null) {
@@ -3771,11 +3772,15 @@
         compiler.internalError(
             'rethrowableException should not be null', node: node);
       }
-      close(new HThrow(exception, isRethrow: true));
+      block = close(new HThrow(exception, isRethrow: true));
     } else {
       visit(node.expression);
-      close(new HThrow(pop()));
+      block = close(new HThrow(pop()));
     }
+    HBasicBlock newBlock = addNewBlock();
+    block.addSuccessor(newBlock);
+    open(newBlock);
+    stack.add(graph.addConstantNull(constantSystem));
   }
 
   visitTypeAnnotation(TypeAnnotation node) {