[MD Bookmarks] Add toasts.

ui/webui/resources/cr_elements_resources.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <grit-part>
   <!-- Polymer 1.0 Elements -->
   <structure name="IDR_CR_ELEMENTS_CR_ACTION_MENU_HTML"
              file="../../webui/resources/cr_elements/cr_action_menu/cr_action_menu.html"
              type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_ACTION_MENU_JS"
              file="../../webui/resources/cr_elements/cr_action_menu/cr_action_menu.js"
              type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_SCROLLABLE_BEHAVIOR_HTML"
@@ skipping 134 matching lines @@
   <structure name="IDR_CR_ELEMENTS_CR_SHARED_STYLE_CSS_HTML"
              file="../../webui/resources/cr_elements/shared_style_css.html"
              type="chrome_html"
              flattenhtml="true" />
   <structure name="IDR_CR_ELEMENTS_CR_HIDDEN_STYLE_CSS_HTML"
              file="../../webui/resources/cr_elements/hidden_style_css.html"
              type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_SHARED_VARS_CSS_HTML"
              file="../../webui/resources/cr_elements/shared_vars_css.html"
              type="chrome_html" />
+  <structure name="IDR_CR_ELEMENTS_CR_TOAST_HTML"
+             file="../../webui/resources/cr_elements/cr_toast/cr_toast.html"

[dpapad, 2017/05/31 17:52:38]

Are those files supposed to be added in the same CL? I could not find another CL
already adding them.

Generally, when adding new elements, we've been adding them where their are
being used (chrome/browser/resources/md_bookmarks) first, and only promote them
to
ui/webui/resources/cr_elements/ once the need to use those elements from a 2nd
WebUI page occurs.

The main benefit of this approach is that 
 - we don't end up with cr_elements that are only used by a single page
indefinitely 
 - cr_elements/ proven that they are "re-usable" since they have 2+ clients.

For example, if someone where to re-use cr_toast.html, might find that
toast_manager.html is also useful/needed, and therefore it would (maybe) make
sense to also put toast_manager.html in cr_elements. This decision is easier to
make once 2nd usage of "toast" is identified.

[calamity, 2017/06/01 06:40:08]

Oops, forgot to git add. I've moved the toast to md_bookmarks/ (and actually
added it this time).

+             type="chrome_html" />
+  <structure name="IDR_CR_ELEMENTS_CR_TOAST_JS"
+             file="../../webui/resources/cr_elements/cr_toast/cr_toast.js"
+             type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_TOOLBAR_HTML"
              file="../../webui/resources/cr_elements/cr_toolbar/cr_toolbar.html"
              type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_TOOLBAR_JS"
              file="../../webui/resources/cr_elements/cr_toolbar/cr_toolbar.js"
              type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_TOOLBAR_SEARCH_FIELD_HTML"
              file="../../webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.html"
              type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_TOOLBAR_SEARCH_FIELD_JS"
              file="../../webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js"
              type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_TOOLBAR_SELECTION_OVERLAY_HTML"
              file="../../webui/resources/cr_elements/cr_toolbar/cr_toolbar_selection_overlay.html"
              type="chrome_html" />
   <structure name="IDR_CR_ELEMENTS_CR_TOOLBAR_SELECTION_OVERLAY_JS"
              file="../../webui/resources/cr_elements/cr_toolbar/cr_toolbar_selection_overlay.js"
              type="chrome_html" />
 </grit-part>