Android: Do not build files not needed on the platform.

This gives us the size decreases from  https://crbug.com/159847#c39

BUG=159847

Review URL: https://codereview.chromium.org/1371863002

Cr-Commit-Position: refs/heads/master@{#351137}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index f66bb8b..1219a47 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -1104,6 +1104,15 @@
     ]
   }
 
+  if (is_android) {
+    sources -= [
+      "sessions/session_service_test_helper.cc",
+      "sessions/session_service_test_helper.h",
+      "ui/webui/signin/login_ui_test_utils.cc",
+      "ui/webui/signin/login_ui_test_utils.h",
+    ]
+  }
+
   if (enable_extensions) {
     sources += [
       "extensions/extension_action_test_util.cc",