Add fast --HEAD option to upstream-diff.

This is useful for large repos (like src.git)

R=agable@chromium.org, szager@chromium.org
BUG=

Review URL: https://codereview.chromium.org/270503003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@269079 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/man/html/git-upstream-diff.html b/man/html/git-upstream-diff.html
index 7d661d4..220f601 100644
--- a/man/html/git-upstream-diff.html
+++ b/man/html/git-upstream-diff.html
@@ -825,6 +825,17 @@
 </p>
 </dd>
 <dt class="hdlist1">
+<code>--staged</code>
+</dt>
+<dd>
+<p>
+  Diff against the staged (cached) changes, instead of against the working
+  directory. This is <em>substantially</em> faster on large repos, but doesn&#8217;t take
+  into account unstaged changes (i.e. changes in your working copy which you
+  haven&#8217;t staged with <code>git add</code>).
+</p>
+</dd>
+<dt class="hdlist1">
 <code>-- &lt;filename patterns&gt;*</code>
 </dt>
 <dd>
@@ -880,7 +891,7 @@
 <div id="footnotes"><hr /></div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2014-04-10 14:23:11 PDT
+Last updated 2014-05-07 00:44:20 PDT
 </div>
 </div>
 </body>