Download doclava when building for Android and use to build cronet Javadocs

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index f64f0f1d5a949e3cf29ea8e0496c881ab16aa3fe..0515e178dd4cd83225dc9d018844d86d12573704 100644
--- a/DEPS
+++ b/DEPS
@@ -815,6 +815,14 @@ hooks = [
     'action': ['python', 'src/third_party/instrumented_libraries/scripts/download_binaries.py'],
   },
   {
+    # Pull doclava binaries if GYP_DEFINES indicate building for Android.
+    'name': 'doclava',
+    'pattern': '.',
+    'action': ['python',
+               'src/build/android/download_doclava.py',
+    ],
+  },
+  {
     # Ensure that while generating dependencies lists in .gyp files we don't
     # accidentally reference any .pyc files whose corresponding .py files have
     # already been deleted.