[iOS][eg2] Convert showcase egtest to EG2.

This CL
 - adds the source file to sources list,
 - makes test source file be backward compatible with EG1,
 - adds required gn dependencies,
 - links to both eg1 and eg2 frameworks.

Bug: 866147
Change-Id: I5c6dc64c783db7a8863c53e69174257e35b719bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1897830
Commit-Queue: Nazerke Kalidolda <nazerke@google.com>
Auto-Submit: Nazerke Kalidolda <nazerke@google.com>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712538}

ios/showcase/core/BUILD.gn

@@ -66,12 +66,14 @@ source_set("main") {
 }
 
 source_set("eg_tests") {
+  defines = [ "CHROME_EARL_GREY_1" ]
   testonly = true
   sources = [
     "showcase_egtest.mm",
   ]
   deps = [
     "//ios/showcase/test",
+    "//ios/testing/earl_grey:earl_grey_support",
     "//ios/third_party/earl_grey:earl_grey+link",
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
@@ -84,9 +86,12 @@ source_set("eg2_tests") {
     "//build/config/ios:xctest_config",
   ]
   testonly = true
-  sources = []
+  sources = [
+    "showcase_egtest.mm",
+  ]
   deps = [
     "//ios/chrome/test/earl_grey:eg_test_support+eg2",
+    "//ios/showcase/test:eg2_test",
     "//ios/testing/earl_grey:eg_test_support+eg2",
     "//ios/third_party/earl_grey2:test_lib",
   ]

ios/showcase/core/showcase_egtest.mm

@@ -2,9 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#import <EarlGrey/EarlGrey.h>
-
 #import "ios/showcase/test/showcase_test_case.h"
+#import "ios/testing/earl_grey/earl_grey_test.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."