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

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 34a21cef91a90a3cd263f8524d68fb8742e129e3..57f0dc90df0d2242e5112a5eaaa248023bc60d50 100644
--- a/DEPS
+++ b/DEPS
@@ -840,6 +840,14 @@ hooks = [
     'action': ['python', 'src/third_party/instrumented_libraries/scripts/download_binaries.py'],
   },
   {
+    # Pull doclava binaries if building for Android.
+    'name': 'doclava',
+    'pattern': '.',
+    'action': ['python',
+               'src/build/android/download_doclava.py',
+    ],
+  },
+  {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     'name': 'gyp',
     'pattern': '.',