Add support for building the Dart VM for Android OS.

tools/utils.py

Index: tools/utils.py
diff --git a/tools/utils.py b/tools/utils.py
index 36ad7e1567dedaedd6121e5a88dfba68bb4623c7..b511a5aabdf29154dc8074d3c6d1cbb8e4be0e0b 100644
--- a/tools/utils.py
+++ b/tools/utils.py
@@ -135,12 +135,12 @@ def GetBuildConf(mode, arch):
 ARCH_GUESS = GuessArchitecture()
 BASE_DIR = os.path.abspath(os.path.join(os.curdir, '..'))
 
-def GetBuildRoot(target_os, mode=None, arch=None):
+def GetBuildRoot(host_os, mode=None, arch=None):
   global BUILD_ROOT
   if mode:
-    return os.path.join(BUILD_ROOT[target_os], GetBuildConf(mode, arch))
+    return os.path.join(BUILD_ROOT[host_os], GetBuildConf(mode, arch))
   else:
-    return BUILD_ROOT[target_os]
+    return BUILD_ROOT[host_os]
 
 def GetBaseDir():
   return BASE_DIR