https://bugs.webkit.org/show_bug.cgi?id=24285
        Text resource loading checks for BOM twice

        This removes TextDecoder class, since its only purpose was to check for BOM, which is
        already done in TextResourceDecoder. Callers that use TextEncoding::decode() won't get
        BOM checked, but I didn't find any cases where it would significantly change behavior.

        * GNUmakefile.am:
        * WebCore.pro:
        * WebCore.scons:
        * WebCore.vcproj/WebCore.vcproj:
        * WebCore.xcodeproj/project.pbxproj:
        * WebCoreSources.bkl:
        Remove TextDecoder.{h,cpp}.

        * platform/text/TextDecoder.cpp: Removed.
        * platform/text/TextDecoder.h: Removed.

        * loader/TextResourceDecoder.h: Instead of a TextDecoder object, keep TextEncoding and
        TextCodec separately.

        * loader/TextResourceDecoder.cpp:
        (WebCore::TextResourceDecoder::TextResourceDecoder): Updated for m_encoding being a member.
        (WebCore::TextResourceDecoder::setEncoding): Ditto.
        (WebCore::TextResourceDecoder::checkForBOM): Removed a FIXME saying that a BOM could override
        even a user-chosen encoding - this is how it already worked due to TextDecoder checking for
        BOM again. Made this function return the detected BOM length.
        (WebCore::TextResourceDecoder::decode): Skip the BOM if it was found at the beginning of
        a text resource.
        (WebCore::TextResourceDecoder::flush): Reset m_checkedForBOM, so that re-decoding the same
        resource again (as frequently done by CachedResource subclasses) will skip the BOM correctly.

        * platform/text/TextEncoding.cpp: (WebCore::TextEncoding::decode):
        Use TextCodec directly without a TextDecoder wrapper. This means that this method no longer
        checks for BOM, which was a counter-intuitive feature.

        * loader/CachedScript.cpp:
        (WebCore::CachedScript::CachedScript):
        (WebCore::CachedScript::setEncoding):
        (WebCore::CachedScript::encoding):
        (WebCore::CachedScript::script):
        * loader/CachedScript.h:
        * loader/appcache/ManifestParser.cpp:
        (WebCore::parseManifest):
        Use TextResourceDecoder, as TextEncoding::decode() no longer checks for BOM.
        A side effect of this is that these resources will now be subject to encoding auto-detection.

        * loader/CachedFont.cpp: (WebCore::CachedFont::ensureSVGFontData):
        * page/Page.cpp: (WebCore::Page::userStyleSheet):
        Be sure to flush TextResourceDecoder, pushing any remaining bytes out, and making the decoder
        re-usable (for repeated decoding of the same resource).

        * platform/text/TextEncodingRegistry.h: Updated comments for newTextCodec().



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@41551 268f45cc-cd09-0410-ab3c-d52691b4dbfc