Add support for building the Dart VM for Android OS.

runtime/third_party/double-conversion/src/double-conversion.gypi

Index: runtime/third_party/double-conversion/src/double-conversion.gypi
diff --git a/runtime/third_party/double-conversion/src/double-conversion.gypi b/runtime/third_party/double-conversion/src/double-conversion.gypi
index 8466d5d66045cf4610489466207c9147774b5142..d411ebd7114234d982bb4d5e08ce33b5b9a45ef6 100644
--- a/runtime/third_party/double-conversion/src/double-conversion.gypi
+++ b/runtime/third_party/double-conversion/src/double-conversion.gypi
@@ -30,6 +30,13 @@
         'strtod.h',
         'utils.h',
       ],
+      'conditions': [
+            ['dart_want_separate_host_toolset==1', {
+              'toolsets': ['host', 'target'],
+            }, {
+              'toolsets': ['target'],
+            }]
+      ],
     },
   ],
 }