Remove code supporting incremental compilation in dart2js

pkg/compiler/lib/src/js_emitter/program_builder/collector.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js.js_emitter.program_builder;
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
@@ skipping 127 matching lines @@
             if (needsAccessor && backend.isAccessibleByReflection(member)) {
               backend.retainMetadataOf(member);
             }
           });
         }
       }
       typedefsNeededForReflection.forEach(backend.retainMetadataOf);
     }
 
     JavaScriptConstantCompiler handler = backend.constants;
-    List<ConstantValue> constants = handler.getConstantsForEmission(
-        compiler.options.hasIncrementalSupport
-            ? null
-            : emitter.compareConstants);
+    List<ConstantValue> constants =
+        handler.getConstantsForEmission(emitter.compareConstants);
     for (ConstantValue constant in constants) {
       if (emitter.isConstantInlinedOrAlreadyEmitted(constant)) continue;
 
       if (constant.isList) outputContainsConstantList = true;
 
       OutputUnit constantUnit =
           compiler.deferredLoadTask.outputUnitForConstant(constant);
       if (constantUnit == null) {
         // The back-end introduces some constants, like "InterceptorConstant" or
         // some list constants. They are emitted in the main output-unit.
@@ skipping 162 matching lines @@
   }
 
   void collect() {
     computeNeededDeclarations();
     computeNeededConstants();
     computeNeededStatics();
     computeNeededStaticNonFinalFields();
     computeNeededLibraries();
   }
 }