Allow root build dependencies to be overridden.

RISK=P2
TESTED=manual
R=andrew@webrtc.org, thorcarpenter@google.com

Review URL: https://webrtc-codereview.appspot.com/19009004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6839 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/all.gyp b/all.gyp
index 4830c54..19c5dea 100644
--- a/all.gyp
+++ b/all.gyp
@@ -10,16 +10,19 @@
   'variables': {
     'libjingle_root%': '<(DEPTH)',
     'include_tests%': 1,
+    'webrtc_root_all_dependencies': [
+      'third_party/openmax_dl/dl/dl.gyp:*',
+      'webrtc/webrtc.gyp:*',
+      '<(DEPTH)/talk/libjingle.gyp:*',
+      '<(DEPTH)/talk/libjingle_examples.gyp:*',
+    ],
   },
   'targets': [
     {
       'target_name': 'All',
       'type': 'none',
       'dependencies': [
-        'third_party/openmax_dl/dl/dl.gyp:*',
-        'webrtc/webrtc.gyp:*',
-        '<(libjingle_root)/talk/libjingle.gyp:*',
-        '<(libjingle_root)/talk/libjingle_examples.gyp:*',
+        '<@(webrtc_root_all_dependencies)',
       ],
       'conditions': [
         ['OS=="android"', {