Change static library targets in safe_json GN files to source sets.

components/safe_json/BUILD.gn

Index: components/safe_json/BUILD.gn
diff --git a/components/safe_json/BUILD.gn b/components/safe_json/BUILD.gn
index 09ce9ad26985f31b062eee2443fd8218715038e9..a57efcc6fdb8fa5be1597103c69d87bddfb0889c 100644
--- a/components/safe_json/BUILD.gn
+++ b/components/safe_json/BUILD.gn
@@ -3,7 +3,7 @@
 # found in the LICENSE file.
 
 # GYP version: components/safe_json.gypi:safe_json
-static_library("safe_json") {
+source_set("safe_json") {
   sources = [
     "safe_json_parser.cc",
     "safe_json_parser.h",
@@ -11,8 +11,6 @@ static_library("safe_json") {
     "safe_json_parser_impl.h",
   ]
 
-  defines = [ "SAFE_JSON_IMPLEMENTATION" ]
-
   deps = [
     ":safe_json_parser_message_filter",
     "//base",
@@ -37,7 +35,7 @@ source_set("test_support") {
 }
 
 # GYP version: components/safe_json.gypi:safe_json_parser_message_filter
-static_library("safe_json_parser_message_filter") {
+source_set("safe_json_parser_message_filter") {
   sources = [
     "safe_json_parser_message_filter.cc",
     "safe_json_parser_message_filter.h",