Add the backchannel for Blobs to be received into Blink from the database backend.

Source/modules/indexeddb/IDBCursor.cpp

Index: Source/modules/indexeddb/IDBCursor.cpp
diff --git a/Source/modules/indexeddb/IDBCursor.cpp b/Source/modules/indexeddb/IDBCursor.cpp
index 0bad4b057c3ccf7b02a3ec547345e69260da7b7e..9fb73bd4be36ed3fe1fb9f04f721d2be48586522 100644
--- a/Source/modules/indexeddb/IDBCursor.cpp
+++ b/Source/modules/indexeddb/IDBCursor.cpp
@@ -38,6 +38,7 @@
 #include "modules/indexeddb/IDBTracing.h"
 #include "modules/indexeddb/IDBTransaction.h"
 #include "modules/indexeddb/WebIDBCallbacksImpl.h"
+#include "public/platform/WebBlobInfo.h"
 #include "public/platform/WebIDBDatabase.h"
 #include "public/platform/WebIDBKeyRange.h"
 #include <limits>
@@ -96,6 +97,7 @@ IDBCursor::IDBCursor(PassOwnPtr<blink::WebIDBCursor> backend, WebIDBCursor::Dire
 
 IDBCursor::~IDBCursor()
 {
+    handleBlobAcks();
 }
 
 PassRefPtr<IDBRequest> IDBCursor::update(ExecutionContext* executionContext, ScriptValue& value, ExceptionState& exceptionState)
@@ -291,6 +293,7 @@ void IDBCursor::close()
 {
     // The notifier may be the last reference to this cursor.
     RefPtr<IDBCursor> protect(this);
+    handleBlobAcks();
     m_request.clear();
     m_backend.clear();
 }
@@ -305,6 +308,7 @@ void IDBCursor::checkForReferenceCycle()
     if (!hasOneRef() || !m_request->hasOneRef())
         return;
 
+    handleBlobAcks();
     m_request.clear();
 }
 
@@ -328,16 +332,18 @@ ScriptValue IDBCursor::value(NewScriptState* scriptState)
     const IDBObjectStoreMetadata& metadata = objectStore->metadata();
     RefPtr<IDBAny> value;
     if (metadata.autoIncrement && !metadata.keyPath.isNull()) {
-        value = IDBAny::create(m_value, m_primaryKey, metadata.keyPath);
+        value = IDBAny::create(m_value, m_blobInfo.get(), m_primaryKey, metadata.keyPath);
 #ifndef NDEBUG
-        assertPrimaryKeyValidOrInjectable(scriptState, m_value, m_primaryKey, metadata.keyPath);
+        assertPrimaryKeyValidOrInjectable(scriptState, m_value, m_blobInfo.get(), m_primaryKey, metadata.keyPath);
 #endif
     } else {
-        value = IDBAny::create(m_value);
+        value = IDBAny::create(m_value, m_blobInfo.get());
     }
 
     m_valueDirty = false;
-    return idbAnyToScriptValue(scriptState, value);
+    ScriptValue scriptValue = idbAnyToScriptValue(scriptState, value);
+    handleBlobAcks();
+    return scriptValue;
 }
 
 ScriptValue IDBCursor::source(NewScriptState* scriptState) const
@@ -345,7 +351,7 @@ ScriptValue IDBCursor::source(NewScriptState* scriptState) const
     return idbAnyToScriptValue(scriptState, m_source);
 }
 
-void IDBCursor::setValueReady(PassRefPtr<IDBKey> key, PassRefPtr<IDBKey> primaryKey, PassRefPtr<SharedBuffer> value)
+void IDBCursor::setValueReady(PassRefPtr<IDBKey> key, PassRefPtr<IDBKey> primaryKey, PassRefPtr<SharedBuffer> value, PassOwnPtr<Vector<blink::WebBlobInfo> > blobInfo)
 {
     m_key = key;
     m_keyDirty = true;
@@ -355,6 +361,7 @@ void IDBCursor::setValueReady(PassRefPtr<IDBKey> key, PassRefPtr<IDBKey> primary
 
     if (isCursorWithValue()) {
         m_value = value;
+        m_blobInfo = blobInfo;

[jsbell, 2014/04/17 19:00:33]

If `value` is never accessed, the blobs remain unacked. If the cursor is
iterated, this overwrites m_blobInfo. Doesn't that mean the previous batch of
blobs won't be acked even when the cursor is freed?

[ericu, 2014/04/17 19:30:14]

Right, thanks; I've added a handleBlobAcks() call before the assignment to fix
it.  This does feel a little fragile, though.  It seems like what I want is a
custom destruction action on some kind of a scoped object, and then I just have
to remember to destroy it after creating the ScriptValue too.  But that seems
rather heavyweight to write just for this.

[jsbell, 2014/04/17 20:19:28]

Yeah. See comment on another review about propagating the IndexedDBValue (bits +
blobs) concept around.

         m_valueDirty = true;
     }
 
@@ -376,6 +383,15 @@ bool IDBCursor::isDeleted() const
     return m_source->idbIndex()->isDeleted();
 }
 
+void IDBCursor::handleBlobAcks()
+{
+    if (m_blobInfo.get() && m_blobInfo->size()) {
+        ASSERT(m_request);

[jsbell, 2014/04/17 19:00:33]

Can we add a complementary ASSERT (outside the if), that if m_request is NULL
there are no blobs to ack?

[ericu, 2014/04/17 19:30:14]

Done.

+        m_request->transaction()->db()->ackReceivedBlobs(m_blobInfo.get());

[jsbell, 2014/04/17 19:00:33]

Can use m_transaction

[ericu, 2014/04/17 19:30:14]

Done.

+        m_blobInfo.clear();
+    }
+}
+
 WebIDBCursor::Direction IDBCursor::stringToDirection(const String& directionString, ExceptionState& exceptionState)
 {
     if (directionString.isNull() || directionString == IDBCursor::directionNext())