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

blimp/common/blob_cache/blob_cache.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BLIMP_COMMON_BLOB_CACHE_BLOB_CACHE_H_
 #define BLIMP_COMMON_BLOB_CACHE_BLOB_CACHE_H_
 
 #include <string>
 #include <vector>
 
 #include "base/memory/ref_counted.h"
 #include "blimp/common/blimp_common_export.h"
 
 namespace blimp {
 
 using BlobId = std::string;
 using BlobData = base::RefCountedData<std::string>;
 
 // Immutable, ref-counted representation of blob payloads, suitable for sharing
 // across threads.
 using BlobDataPtr = scoped_refptr<const BlobData>;
 
 // An interface for a cache of blobs.
 class BLIMP_COMMON_EXPORT BlobCache {
  public:
   virtual ~BlobCache() {}
 
+  // Gets the keys of items stored by the cache.
+  virtual std::vector<BlobId> GetCacheState() const = 0;

[Wez, 2016/06/21 00:33:33]

nit: GetCachedBlobIds()?

[Wez, 2016/06/21 00:33:33]

In general this seems like a potentially large structure to be generating and
returning?

[Kevin M, 2016/06/21 21:23:51]

Done.

[Kevin M, 2016/06/21 21:23:51]

Agreed, but in general I think if this saves us even a few image encodes, the
benefits might outweigh the cost?

I think we can do away with this approach once we get asynchronous image loading
in Skia, since renderer will be able to directly query the browser's cache state
using Contains() and postpone the encode/IPC until it receives a negative
result.

[Wez, 2016/06/22 19:54:23]

Acknowledged.

+
   // Returns true if there is a cache item |id|.
   virtual bool Contains(const BlobId& id) const = 0;
 
   // Stores |data| with the identifier |id| in the cache.
   // Command is ignored if there is already a cache item stored under |id|.
   virtual void Put(const BlobId& id, BlobDataPtr data) = 0;
 
   // Returns a pointer to the cache item |id|, or nullptr if no cache item
   // exists under that identifier.
   virtual BlobDataPtr Get(const BlobId& id) const = 0;
 };
 
 }  // namespace blimp
 
 #endif  // BLIMP_COMMON_BLOB_CACHE_BLOB_CACHE_H_