Minor fixes to junit and robolectric BUILD.gn files.

BUG=

Review URL: https://codereview.chromium.org/1036093002

Cr-Commit-Position: refs/heads/master@{#322508}

testing/android/junit/BUILD.gn

@@ -8,6 +8,7 @@ import("//build/config/android/rules.gni")
 
 # GYP: //testing/android/junit_test.gyp:junit_test_support
 java_library("junit_test_support") {
+  testonly = true
   DEPRECATED_java_in_dir = "java/src"
   deps = [
     "//third_party/junit",
@@ -18,6 +19,7 @@ java_library("junit_test_support") {
 
 # GYP: //testing/android/junit_test.gyp:junit_unit_tests
 java_binary("junit_unittests") {
+  testonly = true
   deps = [
     ":junit_test_support",
     "//third_party/junit",

third_party/junit/BUILD.gn

@@ -11,6 +11,8 @@ java_prebuilt("hamcrest") {
 
 # GYP: //third_party/junit.gyp:junit_jar
 java_library("junit") {
+  chromium_code = false
+  testonly = true
   deps = [
     ":hamcrest",
   ]

third_party/robolectric/BUILD.gn

@@ -6,19 +6,16 @@ import("//build/config/android/rules.gni")
 
 # GYP: //third_party/robolectric/robolectric.gyp:android-all-4.3_r2-robolectric-0
 java_prebuilt("android-all-4.3_r2-robolectric-0") {
-  visibility = [ ":*" ]
   jar_path = "lib/android-all-4.3_r2-robolectric-0.jar"
 }
 
 # GYP: //third_party/robolectric/robolectric.gyp:tagsoup-1.2
 java_prebuilt("tagsoup-1.2") {
-  visibility = [ ":*" ]
   jar_path = "lib/tagsoup-1.2.jar"
 }
 
 # GYP: //third_party/robolectric/robolectric.gyp:json-20080701
 java_prebuilt("json-20080701") {
-  visibility = [ ":*" ]
   jar_path = "lib/json-20080701.jar"
 }