Fix issue 9228, by nopt doing some optimizations in checked mode.

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

 // Copyright (c) 2013, 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;
 
 /**
  * [InvokeDynamicSpecializer] and its subclasses are helpers to
  * optimize intercepted dynamic calls. It knows what input types
  * would be beneficial for performance, and how to change a invoke
@@ skipping 82 matching lines @@
     // The index should be an int when the receiver is a string or array.
     // However it turns out that inserting an integer check in the optimized
     // version is cheaper than having another bailout case. This is true,
     // because the integer check will simply throw if it fails.
     return HType.UNKNOWN;
   }
 
   HInstruction tryConvertToBuiltin(HInvokeDynamic instruction,
                                    Compiler compiler) {
     if (instruction.inputs[1].isMutableIndexable(compiler)) {
+      if (!instruction.inputs[2].isInteger() && compiler.enableTypeAssertions) {
+        // We want the right checked mode error.
+        return null;
+      }
       return new HIndexAssign(instruction.inputs[1],
                               instruction.inputs[2],
                               instruction.inputs[3],
                               instruction.selector);
     }
     return null;
   }
 }
 
 class IndexSpecializer extends InvokeDynamicSpecializer {
@@ skipping 10 matching lines @@
     // The index should be an int when the receiver is a string or array.
     // However it turns out that inserting an integer check in the optimized
     // version is cheaper than having another bailout case. This is true,
     // because the integer check will simply throw if it fails.
     return HType.UNKNOWN;
   }
 
   HInstruction tryConvertToBuiltin(HInvokeDynamic instruction,
                                    Compiler compiler) {
     if (instruction.inputs[1].isIndexable(compiler)) {
+      if (!instruction.inputs[2].isInteger() && compiler.enableTypeAssertions) {
+        // We want the right checked mode error.
+        return null;
+      }
       HInstruction index = new HIndex(
           instruction.inputs[1], instruction.inputs[2], instruction.selector);
       index.instructionType =
           new HType.inferredTypeForSelector(instruction.selector, compiler);
       return index;
     }
     return null;
   }
 }
 
@@ skipping 481 matching lines @@
 
   BinaryOperation operation(ConstantSystem constantSystem) {
     return constantSystem.lessEqual;
   }
 
   HInstruction newBuiltinVariant(HInvokeDynamic instruction) {
     return new HLessEqual(
         instruction.inputs[1], instruction.inputs[2], instruction.selector);
   }
 }