create dartdoc snapshot, add to dart-sdk. Also add resources needed to run dartdoc from the sdk.

sdk/bin/dartdoc.bat

 @echo off
 REM Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 REM for details. All rights reserved. Use of this source code is governed by a
 REM BSD-style license that can be found in the LICENSE file.
 
 setlocal
 rem Handle the case where dart-sdk/bin has been symlinked to.
 set DIR_NAME_WITH_SLASH=%~dp0
 set DIR_NAME=%DIR_NAME_WITH_SLASH:~0,-1%%
 call :follow_links "%DIR_NAME%", RETURNED_BIN_DIR
 rem Get rid of surrounding quotes.
 for %%i in ("%RETURNED_BIN_DIR%") do set BIN_DIR=%%~fi
 
 set DART=%BIN_DIR%\dart
-set SNAPSHOT=%BIN_DIR%\snapshots\dartfmt.dart.snapshot
+set SNAPSHOT=%BIN_DIR%\snapshots\dartdoc.dart.snapshot
 
-"%DART%" "%SNAPSHOT%" %*
+"%DART%" --packages="$BIN_DIR/snapshots/resources/dartdoc/.packages" "%SNAPSHOT%" %*
 
 endlocal
 
 exit /b %errorlevel%
 
 rem Follow the symbolic links (junctions points) using `dir to determine the
 rem canonical path. Output with a link looks something like this
 rem
 rem 01/03/2013  10:11 PM    <JUNCTION>     abc def
 rem [c:\dart_bleeding\dart-repo.9\dart\build\ReleaseIA32\dart-sdk]
 rem
 rem So in the output of 'dir /a:l "targetdir"' we are looking for a filename
 rem surrounded by right angle bracket and left square bracket. Once we get
 rem the filename, which is name of the link, we recursively follow that.
 :follow_links
 setlocal
 for %%i in (%1) do set result=%%~fi
 set current=
 for /f "usebackq tokens=2 delims=[]" %%i in (`dir /a:l "%~dp1" 2^>nul ^
                                              ^| find ">     %~n1 ["`) do (
   set current=%%i
 )
 if not "%current%"=="" call :follow_links "%current%", result
 endlocal & set %~2=%result%
 goto :eof
 
 :end