Make RegExp's constructor non-const.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart b/sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
index b416c3fecbb98e23be5d2912a7a242f4bf5e2ac1..c17883802f2c391bf61603339f9a00183110507a 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
@@ -445,6 +445,7 @@ class VariableNamer {
   final Map<Element, String> parameterNames;
   final List<String> freeTemporaryNames;
   int temporaryIndex = 0;
+  static final RegExp regexp = new RegExp('t[0-9]+');
 
   VariableNamer(LiveEnvironment environment, this.names, this.parameterNames)
     : usedNames = new Set<String>(),
@@ -550,7 +551,6 @@ class VariableNamer {
   void freeName(HInstruction instruction) {
     String ownName = names.ownName[instruction];
     if (ownName != null) {
-      RegExp regexp = const RegExp('t[0-9]+');
       // We check if we have already looked for temporary names
       // because if we haven't, chances are the temporary we allocate
       // in this block can match a phi with the same name in the