fix(dialog): correct the opening position when opening from a button

Closes #757. Closes #746.

Thanks @filod.

Author: ajoslin

src/components/dialog/dialog.js

@@ -418,16 +418,16 @@ function MdDialogProvider($$interimElementProvider) {
       if (clickElement) {
         var clickRect = clickElement[0].getBoundingClientRect();
         startPos = 'translate3d(' +
-          (clickRect.left - element[0].offsetWidth) + 'px,' +
-          (clickRect.top - element[0].offsetHeight) + 'px,' +
+          (clickRect.left - element[0].offsetWidth / 2) + 'px,' +
+          (clickRect.top - element[0].offsetHeight / 2) + 'px,' +
           '0) scale(0.2)';
       } else {
         startPos = 'translate3d(0,100%,0) scale(0.5)';
       }
 
       element
-      .css($mdConstant.CSS.TRANSFORM, startPos)
-      .css('opacity', 0);
+        .css($mdConstant.CSS.TRANSFORM, startPos)
+        .css('opacity', 0);
 
       $$rAF(function() {
         $$rAF(function() {