Add a basic tutorial for the tools in depot_tools.

docs/src/prep_demo_repo.sh

+#!/bin/bash
+
+NO_AUTOPREP=True
+. common_demo_functions.sh
+
+rm -rf $REMOTE
+mkdir -p $REMOTE
+cd $REMOTE
+
+set_user "remote"
+
+silent git init
+
+WS=build/whitespace_file.txt
+
+mkdir build
+cat > "$WS" <<EOF
+Copyright 2014 The Chromium Authors. All rights reserved.
+Use of this useless file is governed by a BSD-style license that can be
+found in the LICENSE file.
+
+
+This file is used for making non-code changes to trigger buildbot cycles. Make
+any modification below this line.
+
+=====================================================================
+
+Let's make a story. Add one sentence for every commit:
+
+CHÄPTER 1:
+It was a dark and blinky night; the rain fell in torrents -- except at
+occasional intervals, when it was checked by a violent gust of wind which
+swept up the streets (for it is in London that our scene lies), rattling along
+the housetops, and fiercely agitating the scanty flame of the lamps that
+struggled against the elements. A hooded figure emerged.
+
+It was a Domo-Banana.
+
+"What took you so long?", inquired his wife.
+
+Silence. Oblivious to his silence, she continued, "Did Mr. Usagi enjoy the
+waffles you brought him?" "You know him, he's not one to forego a waffle,
+no matter how burnt," he snickered.
+
+The pause was filled with the sound of compile errors.
+
+CHAPTER 2:
+The jelly was as dark as night, and just as runny.
+The Domo-Kun shuddered, remembering the way Mr. Usagi had speared his waffles
+with his fork, watching the runny jelly spread and pool across his plate,
+like the blood of a dying fawn. \"It reminds me of that time --\" he started, as
+his wife cut in quickly: \"-- please. I can't bear to hear it.\". A flury of
+images coming from the past flowed through his mind.
+EOF
+git add "$WS"
+
+c "Always output seccomp error messages to stderr"
+c "ozone: evdev: Filter devices by path"
+c "ContentView->ContentViewCore in ContentViewRenderView"
+c "linux_aura: Use system configuration for middle clicking the titlebar."
+c "[fsp] Add requestUnmount() method together with the request manager."
+c "don't use glibc-specific execinfo.h on uclibc builds"
+c "Make ReflectorImpl use mailboxes"
+
+git tag stage_1
+
+c "Change the Pica load benchmark to listen for the polymer-ready event"
+c "Remove AMD family check for the flapper crypto accelerator."
+c "Temporarily CHECK(trial) in ChromeRenderProcessObserver::OnSetFieldTrialGroup."
+
+echo -e '/Banana\ns/Banana/Kun\nwq' | silent ed "$WS"
+git add "$WS"
+set_user 'local'
+c "Fix terrible typo."
+
+set_user 'remote'
+c "Revert 255617, due to it not tracking use of the link doctor page properly."
+
+cat >> "$WS" <<EOF
+
+"You recall what happened on Mulholland drive?" The ceiling fan rotated slowly
+overhead, barely disturbing the thick cigarette smoke. No doubt was left about
+when the fan was last cleaned.
+
+There was an poignant pause.
+EOF
+git add "$WS"
+set_user 'local'
+c 'Finish chapter 2'
+
+git tag stage_2
+
+cat >> "$WS" <<EOF
+
+CHAPTER 3:
+Hilariousness! This chapter is awesome!
+EOF
+git add "$WS"
+set_user 'remote'
+c "Add best chapter2 ever!"
+
+c "Ensure FS is exited for all not-in-same-page navigations."
+c "Refactor data interchange format."