Revert of Make components source_sets on Android. (patchset #1 id:1 of...

Revert of Make components source_sets on Android. (patchset #1 id:1 of https://codereview.chromium.org/2137023003/ )

Reason for revert:
Speculative, might've broke llvm_force_head_revision=true builds (see comment on the original review).

Original issue's description:
> Make components source_sets on Android.
>
> There was a perf regression reported when components were changed from source sets to static libraries in the non-component build. This patch switches back to source sets on Android only to see what happens to thread_times.key_silk_cases and the build performance.
>
> BUG=619593
>
> Committed: https://crrev.com/89248dc70996f9927292a7fee6911715464e1643
> Cr-Commit-Position: refs/heads/master@{#405056}

TBR=dpranke@chromium.org,brettw@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=619593

Review-Url: https://codereview.chromium.org/2151523002
Cr-Commit-Position: refs/heads/master@{#405152}

build/config/BUILDCONFIG.gn

@@ -639,14 +639,9 @@ template("component") {
     assert(invoker.static_component_type == "static_library" ||
            invoker.static_component_type == "source_set")
     _component_mode = invoker.static_component_type
-  } else if (is_android || !defined(invoker.sources)) {
+  } else if (!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"