Reviewed by Eric Seidel.

        Fix warnings emitted by gcc 4.4.1 on linux in chromium-specific platform graphics files.
        https://bugs.webkit.org/show_bug.cgi?id=38158

        Fixes:
        - replace NULL with 0
        - remove unusued locals
        - add parens around ambiguous looking compound predicates like (a || b && c)

        This also adds a check for x >= 0 to FontLinux.cpp's in this statement:
          if (x < walker.width())
        This is more documentation than anything else since walker.width() returns
        an unsigned the current behavior is that x is promoted to unsigned and as
        long as x + walker.width() is less than 2^31 all negative values of x
        end up wrapping around and not being < walker.width().  This behavior is
        tested by fast/text/international/khmer-selection.html

        * platform/graphics/chromium/FontLinux.cpp:
        (WebCore::adjustTextRenderMode):
        (WebCore::TextRunWalker::TextRunWalker):
        (WebCore::TextRunWalker::length):
        (WebCore::TextRunWalker::width):
        (WebCore::TextRunWalker::getTextRun):
        (WebCore::TextRunWalker::getNormalizedTextRun):
        (WebCore::Font::offsetForPositionForComplexText):
        * platform/graphics/chromium/FontPlatformDataLinux.cpp:
        (WebCore::FontPlatformData::setupPaint):
        * platform/graphics/chromium/HarfbuzzSkia.cpp:
        (WebCore::getOutlinePoint):
        * platform/graphics/skia/GraphicsContext3DSkia.cpp:
        (WebCore::GraphicsContext3D::getImageData):
        * platform/graphics/skia/GraphicsContextSkia.cpp:
        (WebCore::isCoordinateSkiaSafe):
        (WebCore::GraphicsContext::fillRect):
        (WebCore::GraphicsContext::strokePath):
        (WebCore::GraphicsContext::strokeRect):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@58916 268f45cc-cd09-0410-ab3c-d52691b4dbfc