Added readme about performance testing for browser perf setup.

tools/testing/perf_testing/perf_README.txt

+Setup to run all performance tests:
+
+TODO(efortuna): run through these steps again on a clean machine to make sure I
+didn't leave anything out!
+
+Overview:
+ These are the instructions to run a wide variety of performance tests using 
+ dart/tools/testing/perf_testing/create_graph.py. Currently the results are 
+ uploaded to https://dartperf.googleplex.com/. 
+ 
+ A variant of these tests are running on our buildbots to test Chrome and 
+ Firefox (since the buildbots are Linux) that simply ensure that no changes to
+ frog have broken updating the dom, but not for testing performance.
+
+ This file details how to set up configurations for each setup. It is long,
+ because there are many variants depending on what platform you're on, and what
+ you want to set up.
+
+============ Windows Installation =============
+
+Setting up Windows on Mac hardware:
+  If you need to install Windows 7 via dual-boot mac, use BootCamp to install 
+  Windows 7 Professional. You can obtain a copy of Windows 7 (Google internal) 
+  by getting an MSDN subscription via GUTS. When installing via BootCamp, don't 
+  forget to also install the "WindowsSupport" drivers that are optional -- 
+  you'll need them to be able to connect to any wireless network in Windows.
+
+Great! You have a shiny dual-booting machine!
+
+Use the following instructions to set up for Windows builds:
+http://www.chromium.org/developers/how-tos/build-instructions-windows
+
+NOTE: DO NOT USE Visual Studio 2010 to try to build the project!! Right now Dart
+only builds with VS2008 versions!
+
+Then:
+1) Download installer for OpenSSL for Windows via 
+   http://openssl.org/related/binaries.html
+2) Install OpenSSL
+3) Copy the directory OpenSSL-Win32/include/openssl to 
+   C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include
+4) Copy the ***contents*** of the directory OpenSSL-Win32/lib/VC/static/ to 
+   C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\lib
+
+============= All Platforms ================
+
+1) Ensure Python 2.7 is installed and in your path.
+
+2) Install selenium library python bindings
+     (http://pypi.python.org/pypi/selenium)
+
+3) Mac only:
+     Download and install xcode 3.2: 
+     https://developer.apple.com/devcenter/download.action?path=/Developer_Tools/xcode_3.2.6_and_ios_sdk_4.3__final/xcode_3.2.6_and_ios_sdk_4.3.dmg
+       a) Mount dmg
+       b) LION only: At a terminal type:
+       TODO(efortuna): verify
+          $> export COMMAND_LINE_INSTALL=1
+          $> open "/Volumes/Xcode and iOS SDK/Xcode and iOS SDK.mpkg"
+       c) Install.
+
+4) (Mac OS Lion only) Install xcode 4.0 and then run:
+   $> xcode-select -switch /path/to/xcode3.2.6/
+
+5) Ensure Firefox is installed.
+
+If you only want to run the smoketests, you're done! 
+While standing in dart/tools/testing/perf_testing, run 
+$> python create_graph.py -b
+If everything goes well, you'll see it print out "PASS" at the command line.
+
+To continue on to run the performance tests:
+
+6) Ensure Java is installed and in your path. If not, install the  Java jdk 
+   (so that we can run the webdriver server from its jar)
+
+7) Add the following to your DEPS file in all.deps in the "deps = {" section:
+  # Copy of Python appengine latest release version             
+  "dart/third_party/appengine-python/1.5.4":            
+    "http://googleappengine.googlecode.com/svn/trunk/python@199",
+
+8) Download selenium-server-standalone-2.15.0.jar (only to run Safari) 
+   http://selenium.googlecode.com/files/selenium-server-standalone-2.15.0.jar 
+   and run it:
+   $> java -jar selenium-server-standalone-2.15.0.jar
+
+9) Ensure that Chrome, Safari and IE (Windows only) are installed.
+
+10)Download the Chrome Driver: http://code.google.com/p/chromium/downloads/list
+   and make sure it is in your path.
+
+10)Disable pop-up blocking in Safari: 
+   Preferences -> Security -> (unselect) Block pop-up windows.
+
+11)TODO(efortuna): Deal with appengine check in! Run 
+   '../../../third_party/appengine-python/1.5.4/appcfg.py update appengine/' 
+   while standing in dart/tools/testing/perf_tests.
+
+12)Install matplotlib http://matplotlib.sourceforge.net/
+
+13)Pull down benchmarks from internal repo (Google only): 
+   http://chromegw.corp.google.com/viewvc/dash/trunk/internal/browserBenchmarks/README.txt?view=markup
+
+14) Run the tests! While standing in dart/tools/testing/perf_testing, run 
+    $> python create_graph.py --forever --verbose --perfbot 
+    to run all the tests (browser performance, language correctness in the
+    browser, command line performance, and self-hosted compile time and compiled
+    code size). 
+    
+    You can run individual tests by adding the particular option (such as 
+    --language) when running create_graph.py. Type "create_graph.py -h" for a 
+    full list of the options.