Fix boolean conversion bug in dart2js + update JSRegExp accordingly.

pkg/compiler/lib/src/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 visitAwait(HAwait node);
   R visitBitAnd(HBitAnd node);
@@ skipping 1303 matching lines @@
 /// This used for attaching source information to reads of locals.
 class HRef extends HInstruction {
   HRef(HInstruction value, SourceInformation sourceInformation)
       : super([value], value.instructionType) {
     this.sourceInformation = sourceInformation;
   }
 
   HInstruction get value => inputs[0];
 
   @override
+  HInstruction convertType(Compiler compiler, DartType type, int kind) {
+    HInstruction converted = value.convertType(compiler, type, kind);
+    if (converted == value) return this;
+    HTypeConversion conversion = converted;
+    conversion.inputs[0] = this;
+    return conversion;
+  }
+
+  @override
   accept(HVisitor visitor) => visitor.visitRef(this);
 
   String toString() => 'HRef(${value})';
 }
 
 /**
  * Late instructions are used after the main optimization phases.  They capture
  * codegen decisions just prior to generating JavaScript.
  */
 abstract class HLateInstruction extends HInstruction {
@@ skipping 1402 matching lines @@
     return typeExpression.isInterfaceType && inputs.length > 1;
   }
   HInstruction get typeRepresentation => inputs[1];
 
   bool get hasContext {
     return typeExpression.isFunctionType && inputs.length > 1;
   }
   HInstruction get context => inputs[1];
 
   HInstruction convertType(Compiler compiler, DartType type, int kind) {
-    if (typeExpression == type) return this;
+    if (typeExpression == type) {
+      // Don't omit a boolean conversion (which doesn't allow `null`) unless
+      // this type conversion is already a boolean conversion.
+      if (kind != BOOLEAN_CONVERSION_CHECK ||
+          isBooleanConversionCheck) {
+        return this;
+      }
+    }
     return super.convertType(compiler, type, kind);
   }
 
   bool get isCheckedModeCheck {
     return kind == CHECKED_MODE_CHECK
         || kind == BOOLEAN_CONVERSION_CHECK;
   }
   bool get isArgumentTypeCheck => kind == ARGUMENT_TYPE_CHECK;
   bool get isReceiverTypeCheck => kind == RECEIVER_TYPE_CHECK;
   bool get isCastTypeCheck => kind == CAST_TYPE_CHECK;
@@ skipping 512 matching lines @@
 class HDynamicType extends HRuntimeType {
   HDynamicType(DynamicType dartType, TypeMask instructionType)
       : super(const <HInstruction>[], dartType, instructionType);
 
   accept(HVisitor visitor) => visitor.visitDynamicType(this);
 
   int typeCode() => HInstruction.DYNAMIC_TYPE_TYPECODE;
 
   bool typeEquals(HInstruction other) => other is HDynamicType;
 }