New ThisIdentifier expression

This allows member expressions to use the 'this' keyword.

test/spec/ol/expr/expression.test.js

@@ -92,6 +92,12 @@ describe('ol.expr.parse()', function() {
       expect(expr.evaluate(scope)).to.be(42);
     });
 
+    it('parses member expressions in the \'this\' scope', function() {
+      var expr = ol.expr.parse('this.foo');
+      var thisScope = {foo: 'bar'};
+      expect(expr.evaluate(undefined, undefined, thisScope)).to.be('bar');
+    });
+
     it('consumes whitespace as expected', function() {
       var expr = ol.expr.parse(' foo . bar . baz ');
       expect(expr).to.be.a(ol.expr.Member);

test/spec/ol/expr/expressions.test.js

@@ -624,6 +624,25 @@ describe('ol.expr.Not', function() {
 });
 
 
+describe('ol.expr.ThisIdentifier', function() {
+
+  describe('#getInstance()', function() {
+    it('has a getInstance method to return the singleton', function() {
+      expect(ol.expr.ThisIdentifier.getInstance())
+          .to.be.a(ol.expr.ThisIdentifier);
+    });
+  });
+
+  describe('#evaluate()', function() {
+    it('evaluates to the passed scope', function() {
+      expect(ol.expr.ThisIdentifier.getInstance()
+          .evaluate(undefined, undefined, 'foo')).to.be('foo');
+    });
+  });
+
+});
+
+
 goog.require('ol.expr.Call');
 goog.require('ol.expr.Comparison');
 goog.require('ol.expr.ComparisonOp');
@@ -636,3 +655,4 @@ goog.require('ol.expr.Math');
 goog.require('ol.expr.MathOp');
 goog.require('ol.expr.Member');
 goog.require('ol.expr.Not');
+goog.require('ol.expr.ThisIdentifier');