Work around runtime engine deficiencies.

sdk/lib/_internal/compiler/implementation/ssa/codegen.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;
 
 class SsaCodeGeneratorTask extends CompilerTask {
 
   final JavaScriptBackend backend;
 
@@ skipping 1646 matching lines @@
     }
   }
 
   visitFieldGet(HFieldGet node) {
     use(node.receiver);
     Element element = node.element;
     if (element == backend.jsIndexableLength) {
       // We're accessing a native JavaScript property called 'length'
       // on a JS String or a JS array. Therefore, the name of that
       // property should not be mangled.
-      push(new js.PropertyAccess.field(pop(), 'length'), node);
+      if (backend.isTypedArray(
+            node.receiver.instructionType.computeMask(compiler))) {
+        // TODO(12929): Remove this custom code for typed arrays once V8
+        // optimizes their length access.
+        // Do a call to `fetchLength` instead of accessing `length`
+        // directly. Because `fetchLength` is a constant we use its
+        // constant value instead.
+        Element element = compiler.findRequiredElement(
+            compiler.typedDataLibrary, const SourceString('fetchLength'));
+        Constant constant = compiler.constantHandler.compileConstant(element);
+        var jsConstant = backend.emitter.constantReference(constant);
+        push(new js.Call(jsConstant, [pop()]), node);
+      } else {
+        push(new js.PropertyAccess.field(pop(), 'length'), node);
+      }
     } else {
       String name = _fieldPropertyName(element);
       push(new js.PropertyAccess.field(pop(), name), node);
       world.registerFieldGetter(element);
     }
   }
 
   visitFieldSet(HFieldSet node) {
     Element element = node.element;
     world.registerFieldSetter(element);
@@ skipping 1295 matching lines @@
   if (leftType.canBeNull() && rightType.canBeNull()) {
     if (left.isConstantNull() || right.isConstantNull() ||
         (leftType.isPrimitive(compiler) && leftType == rightType)) {
       return '==';
     }
     return null;
   } else {
     return '===';
   }
 }