Build gtest from source rather than using SDK-provided version

build_tools/test_build_tools.py

Index: build_tools/test_build_tools.py
diff --git a/build_tools/test_build_tools.py b/build_tools/test_build_tools.py
index 5712c447a39982346daaaacbd98c8441210eb252..8ff9ae14a369383b4b4cd92464b4663ad3cf6187 100644
--- a/build_tools/test_build_tools.py
+++ b/build_tools/test_build_tools.py
@@ -118,8 +118,8 @@ class TestFindEffectedPackages(unittest.TestCase):
      # list.
      self.assertEqual(
          find_effected_packages(['ports/hello', 'ports/ruby'], True, None),
-         ['hello', 'corelibs', 'glibc-compat', 'ncurses', 'readline', 'zlib',
-          'ruby', 'libtar', 'nacl-spawn', 'ruby-ppapi'])
+         ['hello', 'corelibs', 'gtest', 'glibc-compat', 'ncurses', 'readline',
+          'zlib', 'ruby', 'libtar', 'nacl-spawn', 'ruby-ppapi'])
 
    def test_filter(self):
      effected = find_effected_packages(['ports/corelibs'], True,