Adding support for alternate default wallpaper.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 829ed4ab0276ea13b9531eaa7745c0f9b5e77947..03716eb4f6824f19eb95df9bbd10373c2a392ca6 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -308,6 +308,9 @@
       # disabling depends on the platform.
       'enable_themes%': 1,
 
+      # Uses OEM-specific wallpaper resources on Chrome OS.
+      'use_oem_wallpaper%': 0,
+
       # Enables support for background apps.
       'enable_background%': 1,
 
@@ -651,6 +654,7 @@
     'enable_protector_service%': '<(enable_protector_service)',
     'enable_session_service%': '<(enable_session_service)',
     'enable_themes%': '<(enable_themes)',
+    'use_oem_wallpaper%': '<(use_oem_wallpaper)',
     'enable_background%': '<(enable_background)',
     'linux_use_gold_binary%': '<(linux_use_gold_binary)',
     'linux_use_gold_flags%': '<(linux_use_gold_flags)',
@@ -1270,6 +1274,9 @@
       ['enable_themes==1', {
         'grit_defines': ['-D', 'enable_themes'],
       }],
+      ['use_oem_wallpaper==1', {
+        'grit_defines': ['-D', 'use_oem_wallpaper'],
+      }],
       ['clang_use_chrome_plugins==1 and OS!="win"', {
         'clang_chrome_plugins_flags': [
           '<!@(<(DEPTH)/tools/clang/scripts/plugin_flags.sh)'