[Android] Move testing/android/ to testing/android/native_test/

This will let us put android test code unrelated to native test APK wrapping
elsewhere in testing/android/*.

BUG=

Review URL: https://codereview.chromium.org/1071573003

Cr-Commit-Position: refs/heads/master@{#324512}

• base/BUILD.gn[diff]
• build/apk_test.gypi[diff]
• chrome/test/BUILD.gn[diff]
• content/shell/android/browsertests_apk/content_browser_tests_android.cc[diff]
• content/test/BUILD.gn[diff]
• gpu/BUILD.gn[diff]
• media/BUILD.gn[diff]
• remoting/BUILD.gn[diff]
• sandbox/linux/BUILD.gn[diff]
• testing/android/native_test.gyp[diff]
• testing/android/native_test/BUILD.gn[Renamed from testing/android/BUILD.gn - diff]
• testing/android/native_test/README.chromium[Renamed from testing/android/README.chromium - diff]
• testing/android/native_test/java/AndroidManifest.xml[Renamed from testing/android/java/AndroidManifest.xml - diff]
• testing/android/native_test/java/src/org/chromium/native_test/ChromeNativeTestActivity.java[Renamed from testing/android/java/src/org/chromium/native_test/ChromeNativeTestActivity.java - diff]
• testing/android/native_test/java/src/org/chromium/native_test/ChromeNativeTestInstrumentationTestRunner.java[Renamed from testing/android/java/src/org/chromium/native_test/ChromeNativeTestInstrumentationTestRunner.java - diff]
• testing/android/native_test/native_test_jni_onload.cc[Renamed from testing/android/native_test_jni_onload.cc - diff]
• testing/android/native_test/native_test_launcher.cc[Renamed from testing/android/native_test_launcher.cc - diff]
• testing/android/native_test/native_test_launcher.h[Renamed from testing/android/native_test_launcher.h - diff]
• testing/android/native_test/native_test_util.cc[Renamed from testing/android/native_test_util.cc - diff]
• testing/android/native_test/native_test_util.h[Renamed from testing/android/native_test_util.h - diff]
• testing/test.gni[diff]