Android: Do not build any extensions code except for extensions_constants.

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index ef179040f9a12c5aff7fcfa914e3a575464c13e0..e49cccd0b4de9217f47838c7bf6bcdd9bd3f9e77 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -7,6 +7,7 @@ import("//build/config/ui.gni")
 
 # GYP version: chrome/chrome_tests_unit.gypi:test_support_common
 source_set("test_support") {
+  defines = []
   testonly = true
 
   sources = [
@@ -109,7 +110,6 @@ source_set("test_support") {
 
   if (!is_ios) {
     deps += [
-      "//chrome/common/extensions/api",
       "//chrome/plugin",
       "//chrome/renderer",
       "//chrome/utility",
@@ -122,7 +122,6 @@ source_set("test_support") {
       "//components/captive_portal:test_support",
       "//components/infobars/core",
       "//components/sessions:test_support",
-      "//extensions:test_support",
       "//google_apis:test_support",
       "//ipc:test_support",
       "//media:test_support",
@@ -164,6 +163,17 @@ source_set("test_support") {
   if (toolkit_views) {
     deps += [ "//ui/views:test_support" ]
   }
+
+  if (enable_background) {
+    defines += [ "ENABLE_BACKGROUND=1" ]
+  }
+
+  if (enable_extensions) {
+    deps += [
+      "//chrome/common/extensions/api",
+      "//extensions:test_support",
+    ]
+  }
 }
 
 source_set("test_support_unit") {