Reviewed by David Levin.

        Implement FileWriterSync
        https://bugs.webkit.org/show_bug.cgi?id=49939

        Tests to follow in a separate CL, once the test framework in 47680 goes in.

        Build file changes to add FileWriterBase and FileWriterBaseCallback.
        * CMakeLists.txt:
        * GNUmakefile.am:
        * WebCore.gypi:
        * WebCore.pro:
        * WebCore.vcproj/WebCore.vcproj:
        * WebCore.xcodeproj/project.pbxproj:

        FileWriterSync doesn't turn out to need to be an ActiveDOMObject.
        * bindings/scripts/CodeGeneratorV8.pm:

        Added new AsyncFileWriter::waitForOperationToComplete to enable
        synchronous calls.
        * fileapi/AsyncFileWriter.h:

        Added a way to get a FileSystemSync.
        * fileapi/DOMFileSystemSync.cpp:
        * fileapi/FileEntrySync.cpp:
        * fileapi/FileEntrySync.h:
        * fileapi/FileEntrySync.idl:

        Added an error code for OK, rather than just having 0 everywhere.
        * fileapi/FileError.h:

        Turned FileWriterCallback into FileWriterBaseCallback.
        * fileapi/FileSystemCallbacks.cpp:
        * fileapi/FileSystemCallbacks.h:

        Refactored out a common base class, FileWriterBase, for FileWriter and
        FileWriterSync.
        * fileapi/FileWriter.cpp:
        * fileapi/FileWriter.h:
        * fileapi/FileWriterBase.cpp: Added.
        * fileapi/FileWriterBase.h: Added.
        * fileapi/FileWriterBaseCallback.h: Added.
        * fileapi/FileWriterSync.cpp:
        * fileapi/FileWriterSync.h:

        Small tweaks to deal with the base class refactoring.
        * fileapi/DOMFileSystem.cpp:
        * fileapi/DOMFileSystemSync.h:

        Removed "CallWith=ScriptExecutionContext", as FileWriterSync doesn't actually need it.
        * fileapi/FileWriterSync.idl:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@72715 268f45cc-cd09-0410-ab3c-d52691b4dbfc