ServiceWorker CacheID update

Previous design:
1. The renderer needed all references to the same ServiceWorekrCache* to have the same CacheID.
2. The renderer would only send an IPC that a CacheID was deleted when the last reference to the CacheID was deleted in javascript.

After https://codereview.chromium.org/474593002/ and https://codereview.chromium.org/433793002/:
1. The renderer doesn't need all references to the same ServiceWorkerCache* to have the same CacheID.
2. The renderer will send an IPC that a CacheID is deleted after each javascript cache object is deleted.

To address the change on the browser side, simply make a new CacheID for every call to GetCache and CreateCache and delete its corresponding refptr when the CacheID is dropped.

BUG=392621

Review URL: https://codereview.chromium.org/599473002

Cr-Commit-Position: refs/heads/master@{#296390}

content/browser/service_worker/service_worker_cache_listener.cc

@@ -222,25 +222,13 @@ void ServiceWorkerCacheListener::OnCacheStorageKeysCallback(
 ServiceWorkerCacheListener::CacheID
 ServiceWorkerCacheListener::StoreCacheReference(
     const scoped_refptr<ServiceWorkerCache>& cache) {
-  CacheToIDMap::iterator it = cache_to_id_map_.find(cache.get());
-  if (it == cache_to_id_map_.end()) {
-    CacheID cache_id = next_cache_id_++;
-    cache_to_id_map_.insert(std::make_pair(cache.get(), cache_id));
-    id_to_cache_map_.insert(std::make_pair(cache_id, cache));
-    return cache_id;
-  }
-
-  return it->second;
+  int cache_id = next_cache_id_++;
+  id_to_cache_map_[cache_id] = cache;
+  return cache_id;
 }
 
 void ServiceWorkerCacheListener::DropCacheReference(CacheID cache_id) {
-  IDToCacheMap::iterator it = id_to_cache_map_.find(cache_id);
-  if (it != id_to_cache_map_.end())
-    return;
-
-  size_t deleted = cache_to_id_map_.erase(it->second.get());
-  DCHECK(deleted == 1u);
-  id_to_cache_map_.erase(it);
+  id_to_cache_map_.erase(cache_id);
 }
 
 }  // namespace content

content/browser/service_worker/service_worker_cache_listener.h

@@ -40,7 +40,6 @@ class ServiceWorkerCacheListener : public EmbeddedWorkerInstance::Listener {
 
  private:
   typedef int32_t CacheID;  // TODO(jkarlin): Bump to 64 bit.
-  typedef std::map<ServiceWorkerCache*, CacheID> CacheToIDMap;
   typedef std::map<CacheID, scoped_refptr<ServiceWorkerCache> > IDToCacheMap;
 
   void Send(const IPC::Message& message);
@@ -79,7 +78,6 @@ class ServiceWorkerCacheListener : public EmbeddedWorkerInstance::Listener {
   base::WeakPtr<ServiceWorkerContextCore> context_;
 
   IDToCacheMap id_to_cache_map_;
-  CacheToIDMap cache_to_id_map_;
   CacheID next_cache_id_;
 
   base::WeakPtrFactory<ServiceWorkerCacheListener> weak_factory_;