CacheStorage: Don't retain blob handles longer than necessary.

This CL clears our list of BlobDataHandle references after starting the
put operation.  This should reduce how long the references are held
alive since we will no longer have to wait for the
BarrierCallbackForPutResponse objects to be oilpan collected.

Bug: 1133110,1035448
Change-Id: Ibb859da1d1ae31ae4ada588059fe2915058c97a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437911
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812096}

third_party/blink/renderer/modules/cache_storage/cache.cc

@@ -217,6 +217,7 @@ class Cache::BarrierCallbackForPutResponse final
                                      property_name_, interface_name_);
       cache_->PutImpl(resolver_, method_name_, request_list_, response_list_,
                       blob_list_, exception_state, trace_id_);
+      blob_list_.clear();
     }
   }