Make `content` target build without unused data members on Linux.

content/browser/media/webrtc_identity_store.cc

Index: content/browser/media/webrtc_identity_store.cc
diff --git a/content/browser/media/webrtc_identity_store.cc b/content/browser/media/webrtc_identity_store.cc
index 6e9f66dc53d64a89764b2d3a011a15af78f21ebd..2ada2a15f40a358dc150d9c4f3bc5fb485f6ffba 100644
--- a/content/browser/media/webrtc_identity_store.cc
+++ b/content/browser/media/webrtc_identity_store.cc
@@ -137,7 +137,7 @@ class WebRTCIdentityRequestHandle {
   WebRTCIdentityRequestHandle(
       WebRTCIdentityStore* store,
       const WebRTCIdentityStore::CompletionCallback& callback)
-      : store_(store), request_(NULL), callback_(callback) {}
+      : request_(NULL), callback_(callback) {}
 
  private:
   friend class WebRTCIdentityStore;
@@ -172,7 +172,6 @@ class WebRTCIdentityRequestHandle {
     base::ResetAndReturn(&callback_).Run(error, certificate, private_key);
   }
 
-  WebRTCIdentityStore* store_;
   WebRTCIdentityRequest* request_;
   WebRTCIdentityStore::CompletionCallback callback_;