Reviewed by David Levin.

        [chromium] Implement media volume slider for chromium
        https://bugs.webkit.org/show_bug.cgi?id=28715

        Provided the implementation of the volume slider and its container for
        chromium port. With this change there will be a usable volume control
        slider for chromium theme.

        No new tests since this is covered by existing media layout tests.

        * css/mediaControlsChromium.css: CSS style for the volume slider.
        * rendering/RenderThemeChromiumSkia.cpp:
        (WebCore::mediaSliderThumbImage): Returns the image for slider thumb.
        (WebCore::mediaVolumeSliderThumbImage): Returns the image for volume slider thumb.
        (WebCore::RenderThemeChromiumSkia::paintMediaVolumeSliderTrack): Paints the track with one vertical white line.
        (WebCore::RenderThemeChromiumSkia::adjustSliderThumbSize): Adjusts thumb sizes according to the images.
        (WebCore::RenderThemeChromiumSkia::paintMediaSliderThumb): Paints slider thumb image.
        (WebCore::RenderThemeChromiumSkia::paintMediaVolumeSliderThumb): Paints volume slider thumb image.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@47756 268f45cc-cd09-0410-ab3c-d52691b4dbfc