WebUI: Fix compile_js2.py to retrigger compilation for <include> files.

third_party/closure_compiler/compile_js2.gypi

Index: third_party/closure_compiler/compile_js2.gypi
diff --git a/third_party/closure_compiler/compile_js2.gypi b/third_party/closure_compiler/compile_js2.gypi
index 147ab9fc1d508fceb4bb19f5861199bdf5669789..8ab419bd4762ccc0743fd40a4fbcc4052cff0331 100644
--- a/third_party/closure_compiler/compile_js2.gypi
+++ b/third_party/closure_compiler/compile_js2.gypi
@@ -11,6 +11,7 @@
 
     'default_source_file': '<(_target_name).js',
     'source_files%': ['<(default_source_file)'],
+    'extra_inputs%': [],
 
     'includes': ['closure_args.gypi'],
   },
@@ -54,6 +55,9 @@
         '<(CLOSURE_DIR)/include_js.gypi',
         '<(CLOSURE_DIR)/processor.py',
         '>@(_sources)',
+        # When converting to GN, write the paths to additional inputs in a GN
+        # depfile file instead.
+        '<@(extra_inputs)',
       ],
 
       'outputs': ['<(out_file)'],