Ensure _template from behaviors takes precedence over is in legacy.

lib/legacy/class.html

@@ -351,6 +351,15 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         Polymer.LegacyElementMixin(HTMLElement));
       // decorate klass with registration info
       klass.is = info.is;
+      // To match 1.x behavior, `_template` supplied on a behavior should take
+      // precedence over dom-module lookup for `is`; this also prevents
+      // dom-module injection under strictTemplatePolicy for an element that
+      // would normally get its template from a behavior.
+      // TODO(sorvell): Remove once "flattened behaviors" lands, since both
+      // `_template` and `is` will be on the same class after that change
+      if (klass.prototype._template !== undefined) {
+        klass.prototype._template = klass.prototype._template;
+      }
       return klass;
     };
 

test/unit/behaviors.html

@@ -602,8 +602,8 @@ suite('templates from behaviors', function() {
 
   test('template from base', function() {
     var el = fixture('from-base');
-    assert.ok(el.shadowRoot.querySelector('#from-base'));
-    assert.notOk(el.shadowRoot.querySelector('#from-behavior1'));
+    assert.notOk(el.shadowRoot.querySelector('#from-base'));
+    assert.ok(el.shadowRoot.querySelector('#from-behavior1'));
   });
 
   test('template from behavior', function() {