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

blimp/net/blob_channel/blob_channel_sender.h

Index: blimp/net/blob_channel/blob_channel_sender.h
diff --git a/blimp/net/blob_channel/blob_channel_sender.h b/blimp/net/blob_channel/blob_channel_sender.h
index ec121c8f896c2e4bd82494850ff19da1928c5227..c8936e9cc80fd955b1068eef9ddd6b90d3c05204 100644
--- a/blimp/net/blob_channel/blob_channel_sender.h
+++ b/blimp/net/blob_channel/blob_channel_sender.h
@@ -5,6 +5,8 @@
 #ifndef BLIMP_NET_BLOB_CHANNEL_BLOB_CHANNEL_SENDER_H_
 #define BLIMP_NET_BLOB_CHANNEL_BLOB_CHANNEL_SENDER_H_
 
+#include <vector>
+
 #include "blimp/common/blob_cache/blob_cache.h"
 #include "blimp/net/blimp_net_export.h"
 
@@ -12,8 +14,16 @@ namespace blimp {
 
 class BLIMP_NET_EXPORT BlobChannelSender {
  public:
+  struct CacheStateEntry {
+    BlobId id;
+    bool was_delivered;
+  };
+
   virtual ~BlobChannelSender() {}
 
+  // Gets the list of cache keys and their replication status in the BlobCache.
+  virtual std::vector<CacheStateEntry> GetCachedBlobIds() const = 0;
+
   // Puts a blob in the local BlobChannel. The blob can then be pushed to the
   // remote receiver via "DeliverBlob()".
   // Does nothing if there is already a blob |id| in the channel.