Remove DartString from constants.

pkg/compiler/lib/src/compile_time_constants.dart

Index: pkg/compiler/lib/src/compile_time_constants.dart
diff --git a/pkg/compiler/lib/src/compile_time_constants.dart b/pkg/compiler/lib/src/compile_time_constants.dart
index ff674e2b251e25b6e6484aa7534d1717e5fb2ae6..8882e2aeb5463f3f60805c72897130bb36c1da4a 100644
--- a/pkg/compiler/lib/src/compile_time_constants.dart
+++ b/pkg/compiler/lib/src/compile_time_constants.dart
@@ -515,11 +515,9 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
   }
 
   AstConstant visitLiteralString(LiteralString node) {
-    return new AstConstant(
-        context,
-        node,
-        new StringConstantExpression(node.dartString.slowToString()),
-        constantSystem.createString(node.dartString));
+    String text = node.dartString.slowToString();
+    return new AstConstant(context, node, new StringConstantExpression(text),
+        constantSystem.createString(text));
   }
 
   AstConstant visitStringJuxtaposition(StringJuxtaposition node) {
@@ -537,8 +535,8 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
         context,
         node,
         new ConcatenateConstantExpression([left.expression, right.expression]),
-        constantSystem.createString(new DartString.concat(
-            leftValue.primitiveValue, rightValue.primitiveValue)));
+        constantSystem.createString(
+            leftValue.primitiveValue + rightValue.primitiveValue));
   }
 
   AstConstant visitStringInterpolation(StringInterpolation node) {
@@ -548,8 +546,9 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
       return initialString;
     }
     subexpressions.add(initialString.expression);
+    StringBuffer sb = new StringBuffer();
     StringConstantValue initialStringValue = initialString.value;
-    DartString accumulator = initialStringValue.primitiveValue;
+    sb.write(initialStringValue.primitiveValue);
     for (StringInterpolationPart part in node.parts) {
       AstConstant subexpression = evaluate(part.expression);
       if (subexpression == null || subexpression.isError) {
@@ -557,32 +556,25 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
       }
       subexpressions.add(subexpression.expression);
       ConstantValue expression = subexpression.value;
-      DartString expressionString;
-      if (expression.isNum || expression.isBool || expression.isNull) {
+      if (expression.isPrimitive) {
         PrimitiveConstantValue primitive = expression;
-        expressionString =
-            new DartString.literal(primitive.primitiveValue.toString());
-      } else if (expression.isString) {
-        PrimitiveConstantValue primitive = expression;
-        expressionString = primitive.primitiveValue;
+        sb.write(primitive.primitiveValue);
       } else {
         // TODO(johnniwinther): Specialize message to indicated that the problem
         // is not constness but the types of the const expressions.
         return signalNotCompileTimeConstant(part.expression);
       }
-      accumulator = new DartString.concat(accumulator, expressionString);
       AstConstant partString = evaluate(part.string);
       if (partString == null) return null;
       subexpressions.add(partString.expression);
       StringConstantValue partStringValue = partString.value;
-      accumulator =
-          new DartString.concat(accumulator, partStringValue.primitiveValue);
+      sb.write(partStringValue.primitiveValue);
     }
     return new AstConstant(
         context,
         node,
         new ConcatenateConstantExpression(subexpressions),
-        constantSystem.createString(accumulator));
+        constantSystem.createString(sb.toString()));
   }
 
   AstConstant visitLiteralSymbol(LiteralSymbol node) {
@@ -590,7 +582,7 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
     String text = node.slowNameString;
     List<AstConstant> arguments = <AstConstant>[
       new AstConstant(context, node, new StringConstantExpression(text),
-          constantSystem.createString(new LiteralDartString(text)))
+          constantSystem.createString(text))
     ];
     ConstructorElement constructor =
         compiler.commonElements.symbolConstructorTarget;
@@ -668,7 +660,7 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
           AstConstant left = evaluate(send.receiver);
           if (left != null && left.value.isString) {
             StringConstantValue stringConstantValue = left.value;
-            DartString string = stringConstantValue.primitiveValue;
+            String string = stringConstantValue.primitiveValue;
             IntConstantValue length = constantSystem.createInt(string.length);
             result = new AstConstant(context, send,
                 new StringLengthConstantExpression(left.expression), length);
@@ -1043,7 +1035,7 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
           {'fromType': type, 'toType': commonElements.stringType});
     }
 
-    String name = firstArgument.primitiveValue.slowToString();
+    String name = firstArgument.primitiveValue;
     String value = compiler.fromEnvironment(name);
 
     AstConstant createEvaluatedConstant(ConstantValue value) {
@@ -1083,8 +1075,7 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
       }
     } else {
       assert(constructor.isStringFromEnvironmentConstructor);
-      return createEvaluatedConstant(
-          constantSystem.createString(new DartString.literal(value)));
+      return createEvaluatedConstant(constantSystem.createString(value));
     }
   }