Add Mojo IPC for seeding new Renderer with Browser's cached blob state.

blimp/net/blob_channel/blob_channel_sender_impl.cc

Index: blimp/net/blob_channel/blob_channel_sender_impl.cc
diff --git a/blimp/net/blob_channel/blob_channel_sender_impl.cc b/blimp/net/blob_channel/blob_channel_sender_impl.cc
index 4279980f7dd330e3b6e9a93267d2d0b88816d56b..84dec6ccac70d8164800d56a0addeccfaab74349 100644
--- a/blimp/net/blob_channel/blob_channel_sender_impl.cc
+++ b/blimp/net/blob_channel/blob_channel_sender_impl.cc
@@ -4,6 +4,9 @@
 
 #include "blimp/net/blob_channel/blob_channel_sender_impl.h"
 
+#include <utility>
+
+#include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "blimp/common/blob_cache/blob_cache.h"
 #include "blimp/common/blob_cache/id_util.h"
@@ -19,6 +22,21 @@ BlobChannelSenderImpl::BlobChannelSenderImpl(std::unique_ptr<BlobCache> cache,
 
 BlobChannelSenderImpl::~BlobChannelSenderImpl() {}
 
+std::vector<BlobChannelSender::CacheStateEntry>
+BlobChannelSenderImpl::GetCachedBlobIds() const {
+  const auto cache_state = cache_->GetCachedBlobIds();
+  std::vector<CacheStateEntry> output;
+  output.reserve(cache_state.size());
+  for (const std::string& cached_id : cache_state) {
+    CacheStateEntry next_output;
+    next_output.id = cached_id;
+    next_output.was_delivered =
+        ContainsKey(receiver_cache_contents_, cached_id);
+    output.push_back(next_output);
+  }
+  return output;
+}
+
 void BlobChannelSenderImpl::PutBlob(const BlobId& id, BlobDataPtr data) {
   DCHECK(data);
   DCHECK(!id.empty());