gn gen --args='target_os="android"' out/Debug
ninja -C out/Debug components/cronet/android:generate_javadoc

Fails with:
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:24: warning
: no @return
  [javadoc]     public static UploadDataProvider create(final File file) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:39: warning: no @return
  [javadoc]     public static UploadDataProvider create(final ParcelFileDescriptor fd) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:56: warning: no @param for buffer
  [javadoc]     public static UploadDataProvider create(ByteBuffer buffer) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:56: warning: no @return
  [javadoc]     public static UploadDataProvider create(ByteBuffer buffer) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:61: warning: no @param for data
  [javadoc]     public static UploadDataProvider create(byte[] data, int offset, int length) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:61: warning: no @param for offset
  [javadoc]     public static UploadDataProvider create(byte[] data, int offset, int length) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:61: warning: no @param for length
  [javadoc]     public static UploadDataProvider create(byte[] data, int offset, int length) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:61: warning: no @return
  [javadoc]     public static UploadDataProvider create(byte[] data, int offset, int length) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:66: warning: no @param for data
  [javadoc]     public static UploadDataProvider create(byte[] data) {
  [javadoc]                                      ^
  [javadoc] /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/components/cronet/android/api/src/org/chromium/net/UploadDataProviders.java:66: warning: no @return
  [javadoc]     public static UploadDataProvider create(byte[] data) {
  [javadoc]                                      ^
  [javadoc] Building index for all the packages and classes...
  [javadoc] Building index for all classes...
  [javadoc] Generating /usr/local/google/home/agrieve/ssd/git/infra_internal/build/slave/fake_slave/build/src/out/Release/cronet/javadoc/overview-summary.html...
  [javadoc] 10 warnings

BUILD SUCCESSFUL
Total time: 2 seconds

ninja: build stopped: subcommand failed.