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

man/html/git-upstream-diff.html

@@ -825,6 +825,17 @@ so it is disabled by default.</p></div>
 </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 @@ from <a href="https://chromium.googlesource.com/chromium/tools/depot_tools.git">
 <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>

man/man1/git-upstream-diff.1

@@ -2,12 +2,12 @@
 .\"     Title: git-upstream-diff
 .\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
 .\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
-.\"      Date: 04/10/2014
+.\"      Date: 05/07/2014
 .\"    Manual: Chromium depot_tools Manual
-.\"    Source: depot_tools 68b1017
+.\"    Source: depot_tools cab11c5
 .\"  Language: English
 .\"
-.TH "GIT\-UPSTREAM\-DIFF" "1" "04/10/2014" "depot_tools 68b1017" "Chromium depot_tools Manual"
+.TH "GIT\-UPSTREAM\-DIFF" "1" "05/07/2014" "depot_tools cab11c5" "Chromium depot_tools Manual"
 .\" -----------------------------------------------------------------
 .\" * Define some portability stuff
 .\" -----------------------------------------------------------------
@@ -81,6 +81,14 @@ This is particularly useful to show
 files have been changed in comparison to the upstream branch\&.
 .RE
 .PP
+\-\-staged
+.RS 4
+Diff against the staged (cached) changes, instead of against the working directory\&. This is
+\fIsubstantially\fR
+faster on large repos, but doesn\(cqt take into account unstaged changes (i\&.e\&. changes in your working copy which you haven\(cqt staged with
+git add)\&.
+.RE
+.PP
 \-\- <filename patterns>*
 .RS 4
 Restrict the diff to only show the diff for given files compared to the upstream\&.

man/src/git-upstream-diff.txt

@@ -49,6 +49,11 @@ OPTIONS
 `--stat`;;
   This is particularly useful to show 'which' files have been changed in
   comparison to the upstream branch.
+`--staged`;;
+  Diff against the staged (cached) changes, instead of against the working
+  directory. This is 'substantially' faster on large repos, but doesn't take
+  into account unstaged changes (i.e. changes in your working copy which you
+  haven't staged with `git add`).
 `-- <filename patterns>*`;;
   Restrict the diff to only show the diff for given files compared to the
   upstream.