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..ff1c57f1664512492cfd83d97a2928f0aa49fdb2 100644
--- a/blimp/client/core/contents/blimp_contents_manager.cc
+++ b/blimp/client/core/contents/blimp_contents_manager.cc
@@ -97,6 +97,20 @@ BlimpContentsImpl* BlimpContentsManager::GetBlimpContents(int id) {
   return nullptr;
 }
 
+std::vector<BlimpContentsImpl*>
+BlimpContentsManager::GetAllActiveBlimpContents() {
+  std::vector<BlimpContentsImpl*> all_blimp_contents;
+  for (const auto& item : observer_map_) {
+    BlimpContentsImpl* blimp_contents =
+        static_cast<BlimpContentsImpl*>(item.second.get()->blimp_contents());
+    if (!blimp_contents) {
+      continue;
+    }
+    all_blimp_contents.push_back(blimp_contents);
+  }
+  return all_blimp_contents;
+}
+
 int BlimpContentsManager::CreateBlimpContentsId() {
   return next_blimp_contents_id_++;
 }