Try to better guess Visual Studio path when building Dart on Windows.

tools/build.py

Index: tools/build.py
diff --git a/tools/build.py b/tools/build.py
index 84aa62b47f797c258c0b5efffdc50de4c7b2c09c..2c535af8ed3720caf76b91174c32efd51816bfdc 100755
--- a/tools/build.py
+++ b/tools/build.py
@@ -42,8 +42,7 @@ def BuildOptions():
       default=str(HOST_CPUS))
   result.add_option("--devenv",
       help='Path containing devenv.com on Windows',
-      default='C:\\Program Files (x86)\\Microsoft Visual Studio 10.0\\Common7'
-      '\\IDE')
+      default=utils.GuessVisualStudioPath())
   result.add_option("--executable",
       help='Name of the devenv.com/msbuild executable on Windows (varies for '
       'different versions of Visual Studio)', default='devenv.com')

[kustermann, 2013/02/18 21:17:52]

The '--executable' options says that the name of the executable varies for
different versions of visual studio.
I have no idea if this is true. But if it is true, then '--devenv' should
probably be kept in sync with '--executable' (which means that if
'utils.GuessVisualStudioPath()' picks visual studio version X, we need the
executable name corresponding to VS version X as well).

To do this, you could change 'utils.GuessVisualStudioPath()' to return a tuple
like this:

def BuildOptions():
  (vs_directory, vs_executable) = utils.GuessVisualStudioPath()
  result = optparse.OptionParser()
  ....
  result.add_option('--devenv', default=vs_directory, ...)
  result.add_option('--executable', default=vs_executable, ...)

[aam-me, 2013/02/19 04:06:31]

Done.