add 2x header logo and add override to viewport width for landing pages.
changing the viewport to 970 ensures proper layout space for floating divs.

Change-Id: Iea980b4dfe1cca8a2b517f171a847a0e2788b1f0
diff --git a/tools/droiddoc/templates-sdk/components/masthead.cs b/tools/droiddoc/templates-sdk/components/masthead.cs
index 47639bb..3de63ea 100644
--- a/tools/droiddoc/templates-sdk/components/masthead.cs
+++ b/tools/droiddoc/templates-sdk/components/masthead.cs
@@ -6,7 +6,9 @@
         <div class="wrap" id="header-wrap">
           <div class="col-3 logo">
           <a href="<?cs var:toroot ?>index.html">
-            <img src="<?cs var:toroot ?>assets/images/dac_logo.png" width="123" height="25" alt="Android Developers" />
+            <img src="<?cs var:toroot ?>assets/images/dac_logo.png"
+                srcset="<?cs var:toroot ?>assets/images/dac_logo@2x.png 2x"
+                width="123" height="25" alt="Android Developers" />
           </a>
           <div class="btn-quicknav" id="btn-quicknav">
           	<a href="#" class="arrow-inactive">Quicknav</a>