Add dual source blending support for proper blending with coverage.

Review URL: http://codereview.appspot.com/4535088/



git-svn-id: http://skia.googlecode.com/svn/trunk/gyp@1390 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/skia.gyp b/skia.gyp
index 4b0b6ae..7bafbf7 100644
--- a/skia.gyp
+++ b/skia.gyp
@@ -1504,6 +1504,7 @@
         '../samplecode/SampleUnitMapper.cpp',
         '../samplecode/SampleVertices.cpp',
         '../samplecode/SampleXfermodes.cpp',
+        '../samplecode/SampleXfermodesBlur.cpp',
       ],
       'sources!': [
         '../samplecode/SampleSkLayer.cpp', #relies on SkMatrix44 which doesn't compile