IDB: support createIndex/deleteIndex messaging

IDB: support createIndex/deleteIndex messaging
https://bugs.webkit.org/show_bug.cgi?id=127546

Reviewed by Tim Horton.

Source/WebCore:

* WebCore.exp.in: Export a needed CrossThreadCopier

Source/WebKit2:

Message create/delete requests over to the DatabaseProcess, and listen to its replies:
* WebProcess/Databases/IndexedDB/WebIDBServerConnection.cpp:
(WebKit::WebIDBServerConnection::createIndex):
(WebKit::WebIDBServerConnection::didCreateIndex):
(WebKit::WebIDBServerConnection::deleteIndex):
(WebKit::WebIDBServerConnection::didDeleteIndex):
* WebProcess/Databases/IndexedDB/WebIDBServerConnection.h:
* WebProcess/Databases/IndexedDB/WebIDBServerConnection.messages.in:

Pass create/delete requests to the appropriate unique IDB database:
* DatabaseProcess/IndexedDB/DatabaseProcessIDBConnection.cpp:
(WebKit::DatabaseProcessIDBConnection::createIndex):
(WebKit::DatabaseProcessIDBConnection::deleteIndex):
* DatabaseProcess/IndexedDB/DatabaseProcessIDBConnection.h:
* DatabaseProcess/IndexedDB/DatabaseProcessIDBConnection.messages.in:

Message the create/delete request to the database thread for the backing store to handle:
* DatabaseProcess/IndexedDB/UniqueIDBDatabase.cpp:
(WebKit::UniqueIDBDatabase::didCreateIndex):
(WebKit::UniqueIDBDatabase::didDeleteIndex):
(WebKit::UniqueIDBDatabase::createIndex):
(WebKit::UniqueIDBDatabase::deleteIndex):
(WebKit::UniqueIDBDatabase::createIndexInBackingStore):
(WebKit::UniqueIDBDatabase::deleteIndexInBackingStore):
* DatabaseProcess/IndexedDB/UniqueIDBDatabase.h:

* Scripts/webkit2/messages.py:
(struct_or_class):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@162709 268f45cc-cd09-0410-ab3c-d52691b4dbfc