Android: Refactor native test setup in a util class.

This is also needed by content_browsertests.
Also redirecting stdout,stderr for content_browsertests to a fifo file to be read by the test runner scripts.
BUG=138275

TBR=jam@chromium.org

Review URL: https://chromiumcodereview.appspot.com/12213035

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@181587 0039d316-1c4b-4281-b951-d872f2087c98

• content/content_tests.gypi[diff]
• content/shell/android/browsertests_apk/content_browser_tests_android.cc[diff]
• testing/android/native_test.gyp[diff]
• testing/android/native_test_launcher.cc[diff]
• testing/android/native_test_util.cc[Added - diff]
• testing/android/native_test_util.h[Added - diff]