Add Blimp feedback data about visible BlimpContents.

blimp/client/core/contents/blimp_contents_manager.cc

Index: blimp/client/core/contents/blimp_contents_manager.cc
diff --git a/blimp/client/core/contents/blimp_contents_manager.cc b/blimp/client/core/contents/blimp_contents_manager.cc
index 3bf40972fa61917afa087dcb650f8e6867bd7edf..a0d83fb45f3efb2dda68820736582fe9a7efc1ef 100644
--- a/blimp/client/core/contents/blimp_contents_manager.cc
+++ b/blimp/client/core/contents/blimp_contents_manager.cc
@@ -97,6 +97,16 @@ BlimpContentsImpl* BlimpContentsManager::GetBlimpContents(int id) {
   return nullptr;
 }
 
+std::vector<BlimpContentsImpl*>
+BlimpContentsManager::GetAllActiveBlimpContents() {
+  std::vector<BlimpContentsImpl*> all_blimp_contents;
+  for (const auto& item : observer_map_) {
+    all_blimp_contents.push_back(

[David Trainor- moved to gerrit, 2016/09/27 03:49:26]

Check if the contents is null or not.  We do a posttask on removing it from the
map after the destroy call.  So the observer might have a null contents.

[nyquist, 2016/09/27 06:21:29]

Wow! Good catch, thanks! Fixed now. I also of course added a test for this
specific case and verified it fails without the fix, and that the result was as
expected (1 bad entry in return result).

+        static_cast<BlimpContentsImpl*>(item.second.get()->blimp_contents()));
+  }
+  return all_blimp_contents;
+}
+
 int BlimpContentsManager::CreateBlimpContentsId() {
   return next_blimp_contents_id_++;
 }