[iOS] Make chrome_ios_eg2_test template accept invoker's bundle_deps.

This change is fixing an internal test suite which isn't running because
bundle image isn't found. It also enables other test suites add bundle
library they need in the future.

Bug: 1057694
Change-Id: I125ceaece80a852506b9ae9414bf9b3d084d5bf4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2081241
Commit-Queue: Zhaoyang Li <zhaoyangli@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746522}

ios/chrome/test/earl_grey2/chrome_ios_eg2_test.gni

@@ -137,6 +137,7 @@ template("chrome_ios_eg2_test") {
   ios_eg2_test(target_name) {
     forward_variables_from(invoker,
                            [
+                             "bundle_deps",
                              "deps",
                              "data_deps",
                              "executable_args",
@@ -152,7 +153,10 @@ template("chrome_ios_eg2_test") {
     }
     deps += [ "//ios/chrome/test/earl_grey:eg_test_support+eg2" ]
 
-    bundle_deps = [
+    if (!defined(bundle_deps)) {
+      bundle_deps = []
+    }
+    bundle_deps += [
       "//ios/chrome/app/resources",
       "//ios/third_party/gtx:gtx+bundle",
     ]