[MD Extensions] Add Sidebar functionality

Add the missing elements in the sidebar for the developer options, and wire it
up to the Service so that actions like loading unpacked extensions work.
For now, pack extensions doesn't do anything, because we're waiting on the mocks
for the overlay.

BUG=529395

Review URL: https://codereview.chromium.org/1415153005

Cr-Commit-Position: refs/heads/master@{#358753}
diff --git a/chrome/browser/browser_resources.grd b/chrome/browser/browser_resources.grd
index fb60c29..d6097b42 100644
--- a/chrome/browser/browser_resources.grd
+++ b/chrome/browser/browser_resources.grd
@@ -149,6 +149,7 @@
         <include name="IDR_MD_EXTENSIONS_MANAGER_CSS" file="resources\md_extensions\manager.css" type="BINDATA" />
         <include name="IDR_MD_EXTENSIONS_MANAGER_HTML" file="resources\md_extensions\manager.html" type="BINDATA" />
         <include name="IDR_MD_EXTENSIONS_MANAGER_JS" file="resources\md_extensions\manager.js" type="BINDATA" />
+        <include name="IDR_MD_EXTENSIONS_ICONS_HTML" file="resources\md_extensions\icons.html" type="BINDATA" />
         <include name="IDR_MD_EXTENSIONS_ITEM_CSS" file="resources\md_extensions\item.css" type="BINDATA" />
         <include name="IDR_MD_EXTENSIONS_ITEM_HTML" file="resources\md_extensions\item.html" type="BINDATA" />
         <include name="IDR_MD_EXTENSIONS_ITEM_JS" file="resources\md_extensions\item.js" type="BINDATA" />