define icon loader for liunx as separate target

electron.gyp

@@ -328,6 +328,7 @@
         }],  # OS=="mac" and mas_build==1
         ['OS=="linux"', {
           'sources': [
+            '<@(lib_sources_linux)',
             '<@(lib_sources_nss)',
           ],
           'link_settings': {

filenames.gypi

@@ -474,7 +474,6 @@
       'chromium_src/chrome/browser/browser_process.h',
       'chromium_src/chrome/browser/chrome_process_finder_win.cc',
       'chromium_src/chrome/browser/chrome_process_finder_win.h',
-      'chromium_src/chrome/browser/icon_loader_auralinux.cc',
       'chromium_src/chrome/browser/icon_loader_mac.mm',
       'chromium_src/chrome/browser/icon_loader_win.cc',
       'chromium_src/chrome/browser/icon_loader.cc',
@@ -608,6 +607,9 @@
       '<@(native_mate_files)',
       '<(SHARED_INTERMEDIATE_DIR)/atom_natives.h',
     ],
+    'lib_sources_linux': [
+      'chromium_src/chrome/browser/icon_loader_auralinux.cc',
+    ],
     'lib_sources_nss': [
       'chromium_src/chrome/browser/certificate_manager_model.cc',
       'chromium_src/chrome/browser/certificate_manager_model.h',