Import Polymer 0.8 and several key elements.

third_party/polymer/v0_8/components-chromium/polymer/src/lib/template/x-if-extracted.js

Index: third_party/polymer/v0_8/components-chromium/polymer/src/lib/template/x-if-extracted.js
diff --git a/third_party/polymer/v0_8/components-chromium/polymer/src/lib/template/x-if-extracted.js b/third_party/polymer/v0_8/components-chromium/polymer/src/lib/template/x-if-extracted.js
new file mode 100644
index 0000000000000000000000000000000000000000..d8cb6f3275a26675ea41efbc7a52d1c593243cfd
--- /dev/null
+++ b/third_party/polymer/v0_8/components-chromium/polymer/src/lib/template/x-if-extracted.js
@@ -0,0 +1,126 @@
+
+
+  /**
+   * Stamps the template iff the `if` property is truthy.
+   *
+   * When `if` becomes falsey, the stamped content is hidden but not
+   * removed from dom. When `if` subsequently becomes truthy again, the content
+   * is simply re-shown. This approach is used due to its favorable performance
+   * characteristics: the expense of creating template content is paid only 
+   * once and lazily.
+   *
+   * Set the `restamp` property to true to force the stamped content to be
+   * created / destroyed when the `if` condition changes.
+   */
+  Polymer({
+
+    is: 'x-if',
+    extends: 'template',
+
+    properties: {
+
+      'if': {
+        type: Boolean,
+        value: false
+      },
+
+      restamp: {
+        type: Boolean,
+        value: false
+      }
+
+    },
+
+    behaviors: [
+      Polymer.Templatizer
+    ],
+
+    observers: [
+      'render(if, restamp)'
+    ],
+
+    render: function() {
+      this.debounce('render', function() {
+        if (this.if) {
+          if (!this.ctor) {
+            this._wrapTextNodes(this._content);
+            this.templatize(this);
+          }
+          this._ensureInstance();
+        } else if (this.restamp) {
+          this._teardownInstance();
+        }
+        if (!this.restamp && this._instance) {
+          this._showHideInstance(this.if);
+        }
+      });
+    },
+
+    _ensureInstance: function() {
+      if (!this._instance) {
+        // TODO(sorvell): pickup stamping logic from x-repeat
+        this._instance = this.stamp();
+        var root = this._instance.root;
+        this._instance._children = Array.prototype.slice.call(root.childNodes);
+        // TODO(sorvell): this incantation needs to be simpler.
+        var parent = Polymer.dom(Polymer.dom(this).parentNode);
+        parent.insertBefore(root, this);
+      }
+    },
+
+    _teardownInstance: function() {
+      if (this._instance) {
+        var parent = Polymer.dom(Polymer.dom(this).parentNode);
+        this._instance._children.forEach(function(n) {
+          parent.removeChild(n);
+        });
+        this._instance = null;
+      }
+    },
+
+    _wrapTextNodes: function(root) {
+      // wrap text nodes in span so they can be hidden.
+      for (var n = root.firstChild; n; n=n.nextSibling) {
+        if (n.nodeType === Node.TEXT_NODE) {
+          var s = document.createElement('span');
+          root.insertBefore(s, n);
+          s.appendChild(n);
+          n = s;
+        }
+      }
+    },
+
+    // Implements extension point from Templatizer mixin
+    _getStampedChildren: function() {
+      return this._instance._children;
+    },
+
+    _showHideInstance: function(showing) {
+      this._getAllStampedChildren().forEach(function(n) {
+        if (n.setAttribute) {
+          this.serializeValueToAttribute(!showing, 'hidden', n);
+        }
+      }, this);
+    },
+
+    // Implements extension point from Templatizer mixin
+    // Called as side-effect of a host property change, responsible for
+    // notifying parent.<prop> path change on instance
+    _forwardParentProp: function(prop, value) {
+      if (this._instance) {
+        this._instance.parent[prop] = value;
+        this._instance.notifyPath('parent.' + prop, value, true);
+      }
+    },
+
+    // Implements extension point from Templatizer
+    // Called as side-effect of a host path change, responsible for
+    // notifying parent.<path> path change on each row
+    _forwardParentPath: function(path, value) {
+      if (this._instance) {
+        this._instance.notifyPath('parent.' + path, value, true);
+      }
+    }
+
+  });
+