refactor(compiler): extract createCheckBindingStmt into compiler_util

Part of #11683

modules/@angular/compiler/src/compiler_util/binding_util.ts

@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Identifiers, resolveIdentifier} from '../identifiers';
+import {ClassBuilder} from '../output/class_builder';
+import * as o from '../output/output_ast';
+
+import {ConvertPropertyBindingResult} from './expression_converter';
+
+export class CheckBindingField {
+  constructor(public expression: o.ReadPropExpr, public bindingId: string) {}
+}
+
+export function createCheckBindingField(builder: ClassBuilder): CheckBindingField {
+  const bindingId = `${builder.fields.length}`;
+  const fieldExpr = createBindFieldExpr(bindingId);
+  // private is fine here as no child view will reference the cached value...
+  builder.fields.push(new o.ClassField(fieldExpr.name, null, [o.StmtModifier.Private]));
+  builder.ctorStmts.push(o.THIS_EXPR.prop(fieldExpr.name)
+                             .set(o.importExpr(resolveIdentifier(Identifiers.UNINITIALIZED)))
+                             .toStmt());
+  return new CheckBindingField(fieldExpr, bindingId);
+}
+
+export function createCheckBindingStmt(
+    evalResult: ConvertPropertyBindingResult, fieldExpr: o.ReadPropExpr,
+    throwOnChangeVar: o.Expression, actions: o.Statement[]): o.Statement[] {
+  var condition: o.Expression = o.importExpr(resolveIdentifier(Identifiers.checkBinding)).callFn([
+    throwOnChangeVar, fieldExpr, evalResult.currValExpr
+  ]);
+  if (evalResult.forceUpdate) {
+    condition = evalResult.forceUpdate.or(condition);
+  }
+  return [
+    ...evalResult.stmts, new o.IfStmt(condition, actions.concat([
+      <o.Statement>o.THIS_EXPR.prop(fieldExpr.name).set(evalResult.currValExpr).toStmt()
+    ]))
+  ];
+}
+
+function createBindFieldExpr(bindingId: string): o.ReadPropExpr {
+  return o.THIS_EXPR.prop(`_expr_${bindingId}`);
+}