GN: forward_variables_from shouldn't clobber vars.

build/config/android/internal_rules.gni

Index: build/config/android/internal_rules.gni
diff --git a/build/config/android/internal_rules.gni b/build/config/android/internal_rules.gni
index 2c5586c802aa6b9141624f75cdcfa73c0aee9677..f94caac7c05af4af518734673d4530bb282c05f3 100644
--- a/build/config/android/internal_rules.gni
+++ b/build/config/android/internal_rules.gni
@@ -25,7 +25,6 @@ if (is_debug) {
 
 template("android_lint") {
   action(target_name) {
-    deps = []
     forward_variables_from(invoker,
                            [
                              "deps",
@@ -33,6 +32,9 @@ template("android_lint") {
                              "public_deps",
                              "testonly",
                            ])
+    if (!defined(deps)) {
+      deps = []
+    }
     _cache_dir = "$root_build_dir/android_lint_cache"
     _result_path = "$target_gen_dir/$target_name/result.xml"
     _config_path = "$target_gen_dir/$target_name/config.xml"
@@ -386,13 +388,15 @@ template("write_build_config") {
            type == "android_assets" || type == "resource_rewriter" ||
            type == "java_binary" || type == "group")
 
-    deps = []
     forward_variables_from(invoker,
                            [
                              "deps",
                              "testonly",
                              "visibility",
                            ])
+    if (!defined(deps)) {
+      deps = []
+    }
 
     script = "//build/android/gyp/write_build_config.py"
     depfile = "$target_gen_dir/$target_name.d"
@@ -1346,7 +1350,6 @@ template("java_prebuilt_impl") {
   if (defined(invoker.main_class)) {
     _binary_script_target_name = "${_template_name}__java_binary_script"
     java_binary_script(_binary_script_target_name) {
-      deps = []
       forward_variables_from(invoker,
                              [
                                "bootclasspath",
@@ -1354,6 +1357,9 @@ template("java_prebuilt_impl") {
                                "main_class",
                                "wrapper_script_args",
                              ])
+      if (!defined(deps)) {
+        deps = []
+      }
       build_config = _build_config
       jar_path = _jar_path
       script_name = _template_name
@@ -1436,9 +1442,12 @@ template("compile_java") {
     _enable_errorprone = invoker.enable_errorprone
   }
 
-  _enable_incremental_javac = enable_incremental_javac
-  if (defined(invoker.enable_incremental_javac)) {
-    _enable_incremental_javac = invoker.enable_incremental_javac
+  if (defined(invoker.enable_incremental_javac_override)) {
+    # Use invoker-specified override.
+    _enable_incremental_javac = invoker.enable_incremental_javac_override
+  } else {
+    # Default to build arg if not overridden.
+    _enable_incremental_javac = enable_incremental_javac
   }
 
   _manifest_entries = []
@@ -1615,7 +1624,12 @@ template("java_library_impl") {
     _android_manifest = invoker.android_manifest
   }
   assert(_android_manifest != "")  # Mark as used.
-  _run_findbugs = defined(invoker.run_findbugs) && invoker.run_findbugs
+
+  if (defined(invoker.run_findbugs_override)) {
+    _run_findbugs = invoker.run_findbugs_override
+  } else {
+    _run_findbugs = run_findbugs  # Default to build arg if not overridden.
+  }
   assert(_run_findbugs || true)  # Mark as used.
 
   # Don't enable coverage, lint, findbugs unless the target has some
@@ -1701,7 +1715,7 @@ template("java_library_impl") {
                              "alternative_android_sdk_ijar_dep",
                              "dist_jar_path",
                              "enable_errorprone",
-                             "enable_incremental_javac",
+                             "enable_incremental_javac_override",
                              "jar_excluded_patterns",
                              "manifest_entries",
                              "proguard_config",
@@ -1788,12 +1802,14 @@ template("java_library_impl") {
   }
 
   group(target_name) {
-    data_deps = []
     forward_variables_from(invoker,
                            [
                              "data_deps",
                              "visibility",
                            ])
+    if (!defined(data_deps)) {
+      data_deps = []
+    }
     public_deps = _final_deps
     if (_has_lint_target) {
       data_deps += [ ":${_template_name}__analysis" ]
@@ -1952,8 +1968,6 @@ template("process_resources") {
 template("copy_ex") {
   set_sources_assignment_filter([])
   action(target_name) {
-    inputs = []
-    sources = []
     forward_variables_from(invoker,
                            [
                              "data",
@@ -1963,6 +1977,9 @@ template("copy_ex") {
                              "testonly",
                              "visibility",
                            ])
+    if (!defined(sources)) {
+      sources = []
+    }
     script = "//build/android/gyp/copy_ex.py"
 
     depfile = "$target_gen_dir/$target_name.d"
@@ -2099,13 +2116,17 @@ template("test_runner_script") {
       defined(invoker.incremental_install) && invoker.incremental_install
 
   action(target_name) {
-    data_deps = []
-    deps = []
     forward_variables_from(invoker,
                            [
                              "data_deps",
                              "deps",
                            ])
+    if (!defined(deps)) {
+      deps = []
+    }
+    if (!defined(data_deps)) {
+      data_deps = []
+    }
 
     script = "//build/android/gyp/create_test_runner_script.py"
     depfile = "$target_gen_dir/$target_name.d"