Be smarter about when disabling tree-shaking.

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

 // Copyright (c) 2012, 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 ssa;
 
 /**
  * A special element for the extra parameter taken by intercepted
  * methods. We need to override [Element.computeType] because our
  * optimizers may look at its declared type.
@@ skipping 1197 matching lines @@
   }
 
   /**
    * Try to inline [element] within the currect context of the
    * builder. The insertion point is the state of the builder.
    */
   bool tryInlineMethod(Element element,
                        Selector selector,
                        List<HInstruction> providedArguments,
                        Node currentNode) {
+    backend.registerStaticUse(element, compiler.enqueuer.codegen);
     // We cannot inline a method from a deferred library into a method
     // which isn't deferred.
     // TODO(ahe): But we should still inline into the same
     // connected-component of the deferred library.
     if (compiler.deferredLoadTask.isDeferred(element)) return false;
     if (compiler.disableInlining) return false;
     if (inliningStack.length > MAX_INLINING_DEPTH) return false;
 
     // Ensure that [element] is an implementation element.
     element = element.implementation;
@@ skipping 4152 matching lines @@
           new HSubGraphBlockInformation(elseBranch.graph));
 
     HBasicBlock conditionStartBlock = conditionBranch.block;
     conditionStartBlock.setBlockFlow(info, joinBlock);
     SubGraph conditionGraph = conditionBranch.graph;
     HIf branch = conditionGraph.end.last;
     assert(branch is HIf);
     branch.blockInformation = conditionStartBlock.blockFlow;
   }
 }