Update bower.json for Polymer elements and add PRESUBMIT.py

third_party/polymer/v1_0/components-chromium/paper-progress/README.md

 paper-progress
 ===================
 
 The progress bars are for situations where the percentage completed can be
 determined. They give users a quick sense of how much longer an operation
 will take.
 
 Example:
 
 ```html
 <paper-progress value="10"></paper-progress>
 ```
 
 There is also a secondary progress which is useful for displaying intermediate
 progress, such as the buffer level during a streaming playback progress bar.
 
 Example:
 
 ```html
-<paper-progress value="10" secondaryProgress="30"></paper-progress>
+<paper-progress value="10" secondary-progress="30"></paper-progress>
 ```
 
-Styling progress bar:
+### Styling progress bar:
 
 To change the active progress bar color:
 
 ```css
 paper-progress {
   --paper-progress-active-color: #e91e63;
 }
 ```
 
 To change the secondary progress bar color:
 
 ```css
 paper-progress {
   --paper-progress-secondary-color: #f8bbd0;
 }
 ```
 
 To change the progress bar background color:
 
 ```css
 paper-progress {
   --paper-progress-container-color: #64ffda;
 }
 ```
+
+Add the class `transiting` to a `<paper-progress>` to animate the progress bar when
+the value changed. You can also customize the transition:
+
+```css
+paper-progress {
+  --paper-progress-transition-duration: 0.08s;
+  --paper-progress-transition-timing-function: ease;
+  --paper-progress-transition-transition-delay: 0s;
+}
+```