Remove never-happen if statement in WebExternalTextureLayerImpl.

Now this condition never happens after r287686 and BUG=344393
r287686 got rid of lost_resource from this condition.
BUG=344393 made a client never destructed before releasing all mailboxes.

BUG=344393

Review URL: https://codereview.chromium.org/451723002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288157 0039d316-1c4b-4281-b951-d872f2087c98

content/renderer/compositor_bindings/web_external_texture_layer_impl.cc

@@ -113,11 +113,7 @@ void WebExternalTextureLayerImpl::DidReleaseMailbox(
     WebExternalBitmapImpl* bitmap,
     unsigned sync_point,
     bool lost_resource) {
-  if (!layer) {
-    delete bitmap;
-    return;
-  }
-
+  DCHECK(layer);
   blink::WebExternalTextureMailbox available_mailbox;
   memcpy(available_mailbox.name, mailbox.name, sizeof(available_mailbox.name));
   available_mailbox.syncPoint = sync_point;