Add icu as a dependency on Android.

Turns out ICU is referenced by //base/test/BUILD.gn
which is loaded when we generate projects with GN for Android.

This adds ICU back for Android only (was removed in
https://codereview.webrtc.org/1417563006).

TBR=pbos@webrtc.org
NOTRY=true

Review URL: https://codereview.webrtc.org/1414853009

Cr-Commit-Position: refs/heads/master@{#10587}

.gitignore

@@ -94,6 +94,7 @@
 /third_party/gaeunit
 /third_party/gflags/src
 /third_party/google-visualization-python
+/third_party/icu
 /third_party/instrumented_libraries
 /third_party/ijar
 /third_party/jsoncpp

setup_links.py

@@ -84,6 +84,7 @@ if 'android' in target_os:
     'third_party/android_tools',
     'third_party/appurify-python',
     'third_party/ashmem',
+    'third_party/icu',
     'third_party/ijar',
     'third_party/jsr-305',
     'third_party/junit',