Merge CoreTypes and CoreClasses into CommonElements.

pkg/compiler/lib/src/ssa/builder_kernel.dart

Index: pkg/compiler/lib/src/ssa/builder_kernel.dart
diff --git a/pkg/compiler/lib/src/ssa/builder_kernel.dart b/pkg/compiler/lib/src/ssa/builder_kernel.dart
index 2721db9d8e03a206a3c010ed5e1bcd56edb4e880..9295ec60beaa86bde19d5dc0eaff8d74bc82a4b2 100644
--- a/pkg/compiler/lib/src/ssa/builder_kernel.dart
+++ b/pkg/compiler/lib/src/ssa/builder_kernel.dart
@@ -215,7 +215,7 @@ class KernelSsaBuilder extends ir.Visitor with GraphBuilder {
     HInstruction value = pop();
     if (typeBuilder.checkOrTrustTypes) {
       return typeBuilder.potentiallyCheckOrTrustType(
-          value, compiler.coreTypes.boolType,
+          value, compiler.commonElements.boolType,
           kind: HTypeConversion.BOOLEAN_CONVERSION_CHECK);
     }
     HInstruction result = new HBoolify(value, commonMasks.boolType);