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

blimp/engine/renderer/blob_channel_sender_proxy.cc

Index: blimp/engine/renderer/blob_channel_sender_proxy.cc
diff --git a/blimp/engine/renderer/blob_channel_sender_proxy.cc b/blimp/engine/renderer/blob_channel_sender_proxy.cc
index efdfeae668bcd02cc3e329944e7a495559337843..2a5dfd73bdf4190e79d71beabcfdff5d01219785 100644
--- a/blimp/engine/renderer/blob_channel_sender_proxy.cc
+++ b/blimp/engine/renderer/blob_channel_sender_proxy.cc
@@ -22,7 +22,13 @@ mojom::BlobChannelPtr GetConnectedBlobChannel() {
 }  // namespace
 
 BlobChannelSenderProxy::BlobChannelSenderProxy()
-    : blob_channel_(GetConnectedBlobChannel()) {}
+    : blob_channel_(GetConnectedBlobChannel()), weak_factory_(this) {
+  // TODO(kmarshall): Switch to observer push model (vs. the current pull model)
+  // once cache invalidations are introduced.
+  blob_channel_->GetCachedBlobIds(
+      base::Bind(&BlobChannelSenderProxy::OnGetCacheStateComplete,
+                 weak_factory_.GetWeakPtr()));
+}
 
 BlobChannelSenderProxy::~BlobChannelSenderProxy() {}
 
@@ -52,5 +58,21 @@ void BlobChannelSenderProxy::DeliverBlob(const std::string& id) {
   blob_channel_->DeliverBlob(id);
 }
 
+std::vector<BlobChannelSender::CacheStateEntry>
+BlobChannelSenderProxy::GetCachedBlobIds() const {
+  NOTREACHED();
+  return std::vector<BlobChannelSender::CacheStateEntry>();
+}
+
+void BlobChannelSenderProxy::OnGetCacheStateComplete(
+    mojo::Array<mojom::CacheStateEntryPtr> cache_state) {
+  VLOG(1) << "Received cache state from browser (" << cache_state.size()
+          << " items)";
+  replication_state_.clear();

[dcheng, 2016/06/28 21:34:52]

Are there callbacks to update this state later? I'm just wondering if this will
collide with mutations in DeliverBlob() above.

[Kevin M, 2016/06/29 21:01:22]

For now, this is called only once at the beginning of the renderer process'
lifetime, so we don't need to worry about collisions.

As the (temporary, in-memory) cache doesn't yet support evictions, we don't have
to add any listeners for cache invalidation events. When we do implement an
actual cache, we'll have to do it - probably by passing a delegate Interface
that allows the browser to push the cache state delta to the renderer.

+  for (const auto& next_item : cache_state) {
+    replication_state_[next_item->id] = next_item->was_delivered;
+  }
+}
+
 }  // namespace engine
 }  // namespace blimp