Reland of Make components source_sets on Android.

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 4f3a223c32d23ab7b79007add5081deac14bdf7e..2036b3451904718854386ad7b6c6013ebf768033 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -639,9 +639,14 @@
     assert(invoker.static_component_type == "static_library" ||
            invoker.static_component_type == "source_set")
     _component_mode = invoker.static_component_type
-  } else if (!defined(invoker.sources)) {
+  } else if (is_android || !defined(invoker.sources)) {
     # When there are no sources defined, use a source set to avoid creating
     # an empty static library (which generally don't work).
+    #
+    # TODO(brettw) remove the Android condition or comment why it needs to be
+    # kept after some analysis. Source sets vs. static libraries seem to be
+    # causing some performance differences. As part of the analysis for
+    # http://crbug.com/619593 we're testing source sets for components again.
     _component_mode = "source_set"
   } else {
     _component_mode = "static_library"