Add float-to-half (binary16) conversion functions.

gyp/core.gypi

 # Include this gypi to include all 'core' files
 # The parent gyp/gypi file must define
 #       'skia_src_path'     e.g. skia/trunk/src
 #       'skia_include_path' e.g. skia/trunk/include
 #
 # The skia build defines these in common_variables.gypi
 #
 {
     'sources': [
         '<(skia_src_path)/c/sk_surface.cpp',
@@ skipping 83 matching lines @@
         '<(skia_src_path)/core/SkFontHost.cpp',
         '<(skia_src_path)/core/SkFontDescriptor.cpp',
         '<(skia_src_path)/core/SkFontDescriptor.h',
         '<(skia_src_path)/core/SkFontStream.cpp',
         '<(skia_src_path)/core/SkFontStream.h',
         '<(skia_src_path)/core/SkGeometry.cpp',
         '<(skia_src_path)/core/SkGlyphCache.cpp',
         '<(skia_src_path)/core/SkGlyphCache.h',
         '<(skia_src_path)/core/SkGlyphCache_Globals.h',
         '<(skia_src_path)/core/SkGraphics.cpp',
+        '<(skia_src_path)/core/SkHalf.cpp',
+        '<(skia_src_path)/core/SkHalf.h',
         '<(skia_src_path)/core/SkInstCnt.cpp',
         '<(skia_src_path)/core/SkImageFilter.cpp',
         '<(skia_src_path)/core/SkImageInfo.cpp',
         '<(skia_src_path)/core/SkImageGenerator.cpp',
         '<(skia_src_path)/core/SkLayerInfo.h',
         '<(skia_src_path)/core/SkLayerInfo.cpp',
         '<(skia_src_path)/core/SkLocalMatrixShader.cpp',
         '<(skia_src_path)/core/SkLineClipper.cpp',
         '<(skia_src_path)/core/SkMallocPixelRef.cpp',
         '<(skia_src_path)/core/SkMask.cpp',
@@ skipping 258 matching lines @@
         '<(skia_src_path)/pathops/SkPathOpsPoint.h',
         '<(skia_src_path)/pathops/SkPathOpsQuad.h',
         '<(skia_src_path)/pathops/SkPathOpsRect.h',
         '<(skia_src_path)/pathops/SkPathOpsTriangle.h',
         '<(skia_src_path)/pathops/SkPathOpsTypes.h',
         '<(skia_src_path)/pathops/SkPathWriter.h',
         '<(skia_src_path)/pathops/SkQuarticRoot.h',
         '<(skia_src_path)/pathops/SkReduceOrder.h',
     ],
 }