We can actually map the Dart shift right to the JavaScript one under certain conditions.

sdk/lib/_internal/compiler/implementation/ssa/nodes.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;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
@@ skipping 37 matching lines @@
   R visitLoopBranch(HLoopBranch node);
   R visitMultiply(HMultiply node);
   R visitNegate(HNegate node);
   R visitNot(HNot node);
   R visitOneShotInterceptor(HOneShotInterceptor node);
   R visitParameterValue(HParameterValue node);
   R visitPhi(HPhi node);
   R visitRangeConversion(HRangeConversion node);
   R visitReturn(HReturn node);
   R visitShiftLeft(HShiftLeft node);
+  R visitShiftRight(HShiftRight node);
   R visitStatic(HStatic node);
   R visitStaticStore(HStaticStore node);
   R visitStringConcat(HStringConcat node);
   R visitStringify(HStringify node);
   R visitSubtract(HSubtract node);
   R visitSwitch(HSwitch node);
   R visitThis(HThis node);
   R visitThrow(HThrow node);
   R visitThrowExpression(HThrowExpression node);
   R visitTry(HTry node);
@@ skipping 261 matching lines @@
   visitNegate(HNegate node) => visitInvokeUnary(node);
   visitNot(HNot node) => visitInstruction(node);
   visitOneShotInterceptor(HOneShotInterceptor node)
       => visitInvokeDynamic(node);
   visitPhi(HPhi node) => visitInstruction(node);
   visitMultiply(HMultiply node) => visitBinaryArithmetic(node);
   visitParameterValue(HParameterValue node) => visitLocalValue(node);
   visitRangeConversion(HRangeConversion node) => visitCheck(node);
   visitReturn(HReturn node) => visitControlFlow(node);
   visitShiftLeft(HShiftLeft node) => visitBinaryBitOp(node);
+  visitShiftRight(HShiftRight node) => visitBinaryBitOp(node);
   visitSubtract(HSubtract node) => visitBinaryArithmetic(node);
   visitSwitch(HSwitch node) => visitControlFlow(node);
   visitStatic(HStatic node) => visitInstruction(node);
   visitStaticStore(HStaticStore node) => visitInstruction(node);
   visitStringConcat(HStringConcat node) => visitInstruction(node);
   visitStringify(HStringify node) => visitInstruction(node);
   visitThis(HThis node) => visitParameterValue(node);
   visitThrow(HThrow node) => visitControlFlow(node);
   visitThrowExpression(HThrowExpression node) => visitInstruction(node);
   visitTry(HTry node) => visitControlFlow(node);
@@ skipping 445 matching lines @@
   static const int LESS_EQUAL_TYPECODE = 20;
   static const int STATIC_TYPECODE = 21;
   static const int STATIC_STORE_TYPECODE = 22;
   static const int FIELD_GET_TYPECODE = 23;
   static const int TYPE_CONVERSION_TYPECODE = 24;
   static const int TYPE_KNOWN_TYPECODE = 25;
   static const int INVOKE_STATIC_TYPECODE = 26;
   static const int INDEX_TYPECODE = 27;
   static const int IS_TYPECODE = 28;
   static const int INVOKE_DYNAMIC_TYPECODE = 29;
+  static const int SHIFT_RIGHT_TYPECODE = 30;
 
   HInstruction(this.inputs, this.instructionType)
       : id = idCounter++, usedBy = <HInstruction>[] {
     assert(inputs.every((e) => e != null));
   }
 
   int get hashCode => id;
 
   bool useGvn() => _useGvn;
   void setUseGvn() { _useGvn = true; }
@@ skipping 906 matching lines @@
   HShiftLeft(left, right, selector, type) : super(left, right, selector, type);
   accept(HVisitor visitor) => visitor.visitShiftLeft(this);
 
   BinaryOperation operation(ConstantSystem constantSystem)
       => constantSystem.shiftLeft;
   int typeCode() => HInstruction.SHIFT_LEFT_TYPECODE;
   bool typeEquals(other) => other is HShiftLeft;
   bool dataEquals(HInstruction other) => true;
 }
 
+class HShiftRight extends HBinaryBitOp {
+  HShiftRight(left, right, selector, type) : super(left, right, selector, type);
+  accept(HVisitor visitor) => visitor.visitShiftRight(this);
+
+  BinaryOperation operation(ConstantSystem constantSystem)
+      => constantSystem.shiftRight;
+  int typeCode() => HInstruction.SHIFT_RIGHT_TYPECODE;
+  bool typeEquals(other) => other is HShiftRight;
+  bool dataEquals(HInstruction other) => true;
+}
+
 class HBitOr extends HBinaryBitOp {
   HBitOr(left, right, selector, type) : super(left, right, selector, type);
   accept(HVisitor visitor) => visitor.visitBitOr(this);
 
   BinaryOperation operation(ConstantSystem constantSystem)
       => constantSystem.bitOr;
   int typeCode() => HInstruction.BIT_OR_TYPECODE;
   bool typeEquals(other) => other is HBitOr;
   bool dataEquals(HInstruction other) => true;
 }
@@ skipping 1084 matching lines @@
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty);
     return statements.last.end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }