Add support for building the Dart VM for Android OS.

tools/gyp/source_filter.gypi

Index: tools/gyp/source_filter.gypi
diff --git a/tools/gyp/source_filter.gypi b/tools/gyp/source_filter.gypi
index da04091c626da9551c2ec5a0eb45d33905f8ee74..6d37cd03f484965e24b7f77ee2ba3a33f86f9034 100644
--- a/tools/gyp/source_filter.gypi
+++ b/tools/gyp/source_filter.gypi
@@ -5,6 +5,7 @@
 {
   'target_defaults': {
     'conditions': [
+      ['OS!="android"', {'sources/': [['exclude', '_android\\.(cc|h)$']]}],
       ['OS!="linux"', {'sources/': [['exclude', '_linux\\.(cc|h)$']]}],
       ['OS!="mac"', {'sources/': [['exclude', '_macos\\.(cc|h)$']]}],
       ['OS!="win"', {'sources/': [['exclude', '_win\\.(cc|h)$']]}],