Incorporate BlobChannel into Blimp image encode/decode pipeline.

blimp/client/feature/compositor/decoding_image_generator.cc

Index: blimp/client/feature/compositor/decoding_image_generator.cc
diff --git a/blimp/client/feature/compositor/decoding_image_generator.cc b/blimp/client/feature/compositor/decoding_image_generator.cc
index eaa4f9545be347fd9ceae8858beb48ef608dcc8c..d822de65fc08bdf26c497f3a0f8ef0ad3aeb9554 100644
--- a/blimp/client/feature/compositor/decoding_image_generator.cc
+++ b/blimp/client/feature/compositor/decoding_image_generator.cc
@@ -6,6 +6,7 @@
 
 #include "base/numerics/safe_conversions.h"
 #include "blimp/client/feature/compositor/blimp_image_decoder.h"
+#include "blimp/client/feature/compositor/client_image_serialization_processor.h"
 #include "blimp/common/proto/blob_cache.pb.h"
 #include "third_party/libwebp/webp/decode.h"
 #include "third_party/libwebp/webp/demux.h"
@@ -34,7 +35,10 @@ DecodingImageGenerator::DecodingImageGenerator(const SkImageInfo info,
                                                const void* data,
                                                size_t size)
     : SkImageGenerator(info) {
-  BlimpImageDecoder(data, size, &decoded_bitmap_);
+  if (!ClientImageSerializationProcessor::GetInstance()->GetAndDecodeBlob(
+          data, size, &decoded_bitmap_)) {
+    DLOG(WARNING) << "GetAndDecodeBlob failed.";

[Wez, 2016/05/21 01:08:03]

All the failure code paths in GetAndDecodeBlob already log something; suggest
logging inside, or outside, but not both!

If GetAndDecodeBlob fails here then something is seriously wrong - can we
restructure this to allow us to propagate the failure and disconnect the session
in this case?

[Kevin M, 2016/05/27 22:35:29]

Done, see set_error_delegate for error reporting.

Upgraded this to DLOG(FATAL) so that this will break on debug builds when
GetAndDecodeBlob fails.

[Wez, 2016/06/07 01:18:31]

I don't understand why we need the error delegate on the
ClientImageSerializationProcessor - isn't it effectively the same as the false
return-value here, in which case why does this class not handle it?  Why do we
need both the delegate and the return-value?

nit: Seems redundant to say "GetAndDecodeBlob() failed" here - you might just
do:

bool result = GetAndDecodeBlob()
DCHECK(result);

+  }
 }
 
 DecodingImageGenerator::~DecodingImageGenerator() {}