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

blimp/engine/renderer/blob_channel_sender_proxy.h

Index: blimp/engine/renderer/blob_channel_sender_proxy.h
diff --git a/blimp/engine/renderer/blob_channel_sender_proxy.h b/blimp/engine/renderer/blob_channel_sender_proxy.h
index e219ef06c35e7ff5fda51bed6f00343a4bd8ceb7..98b118ed6db90c861148b08dbff432d8576cc84b 100644
--- a/blimp/engine/renderer/blob_channel_sender_proxy.h
+++ b/blimp/engine/renderer/blob_channel_sender_proxy.h
@@ -7,8 +7,10 @@
 
 #include <memory>
 #include <string>
+#include <vector>
 
 #include "base/containers/hash_tables.h"
+#include "base/memory/weak_ptr.h"
 #include "blimp/common/blimp_common_export.h"
 #include "blimp/engine/mojo/blob_channel.mojom.h"
 #include "blimp/net/blob_channel/blob_channel_sender.h"
@@ -20,6 +22,14 @@ namespace engine {
 // process.
 class BLIMP_COMMON_EXPORT BlobChannelSenderProxy : public BlobChannelSender {
  public:
+  // Asynchronously request the set of cache keys from the browser process.
+  // Knowledge of the browser's cache allows the renderer to avoid re-encoding
+  // and re-transferring image assets that are already tracked by the
+  // browser-side cache.
+  //
+  // If |this| is used in the brief time before the response arrives,
+  // the object will continue to work, but false negatives will be returned
+  // for IsInEngineCache() and IsInClientCache().
   BlobChannelSenderProxy();
   ~BlobChannelSenderProxy() override;
 
@@ -30,10 +40,14 @@ class BLIMP_COMMON_EXPORT BlobChannelSenderProxy : public BlobChannelSender {
   bool IsInClientCache(const std::string& id) const;
 
   // BlobChannelSender implementation.
+  std::vector<CacheStateEntry> GetCachedBlobIds() const override;
   void PutBlob(const BlobId& id, BlobDataPtr data) override;
   void DeliverBlob(const BlobId& id) override;
 
  private:
+  void OnGetCacheStateComplete(
+      mojo::Array<mojom::CacheStateEntryPtr> cache_state);
+
   // BlobChannel Mojo IPC stub, used for delivering blobs to the browser
   // process.
   mojom::BlobChannelPtr blob_channel_;
@@ -43,6 +57,8 @@ class BLIMP_COMMON_EXPORT BlobChannelSenderProxy : public BlobChannelSender {
   // image encoding and transferral if the content is already in the system.
   base::hash_map<std::string, bool> replication_state_;
 
+  base::WeakPtrFactory<BlobChannelSenderProxy> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(BlobChannelSenderProxy);
 };