Add src_files to src_jar GN template

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index a26be55dd92487a88efd937f6e8ab16c6e8ebbc8..0d03e36d544c90001a5f38e05b6684d477360684 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -2254,6 +2254,7 @@ if (is_android) {
       ":base_android_java_enums_srcjar",
       ":base_build_config_gen",
       ":base_native_libraries_gen",
+      ":base_java_srcjar",
     ]
 
     deps = [
@@ -2262,7 +2263,18 @@ if (is_android) {
       "//third_party/jsr-305:jsr_305_javalib",
     ]
 
-    java_files = [
+    # New versions of BuildConfig.java and NativeLibraries.java
+    # (with the actual correct values) will be created when creating an apk.
+    jar_excluded_patterns = [
+      "*/BuildConfig.class",
+      "*/NativeLibraries.class",
+      "*/NativeLibraries##*.class",
+    ]
+  }
+
+  # Creates srcjar that contains sources for "base_java".
+  zip("base_java_srcjar") {
+    inputs = [
       "android/java/src/org/chromium/base/ActivityState.java",
       "android/java/src/org/chromium/base/AnimationFrameTimeHistogram.java",
       "android/java/src/org/chromium/base/ApiCompatibilityUtils.java",
@@ -2326,14 +2338,8 @@ if (is_android) {
       "android/java/src/org/chromium/base/metrics/RecordUserAction.java",
       "android/java/src/org/chromium/base/multidex/ChromiumMultiDexInstaller.java",
     ]
-
-    # New versions of BuildConfig.java and NativeLibraries.java
-    # (with the actual correct values) will be created when creating an apk.
-    jar_excluded_patterns = [
-      "*/BuildConfig.class",
-      "*/NativeLibraries.class",
-      "*/NativeLibraries##*.class",
-    ]
+    output = "$target_gen_dir/$target_name.srcjar"
+    base_dir = rebase_path("//base/android/java/src")
   }
 
   # GYP: //base.gyp:base_javatests