Move code in isPaintOpaque from SkDeferredCanvas.cpp to SkPaintPriv

The purpose of this code move is to make it re-usable in order to implement
occlusion culling optimizations in SkPicture similar to what we have now
in SkDeferredCanvas.

BUG=https://code.google.com/p/chromium/issues/detail?id=164530
Review URL: https://codereview.appspot.com/7196046

git-svn-id: http://skia.googlecode.com/svn/trunk@7361 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/core.gypi b/gyp/core.gypi
index 1dc1392..be3bc8e 100644
--- a/gyp/core.gypi
+++ b/gyp/core.gypi
@@ -107,6 +107,8 @@
         '<(skia_src_path)/core/SkOrderedWriteBuffer.cpp',
         '<(skia_src_path)/core/SkPackBits.cpp',
         '<(skia_src_path)/core/SkPaint.cpp',
+        '<(skia_src_path)/core/SkPaintPriv.cpp',
+        '<(skia_src_path)/core/SkPaintPriv.h',
         '<(skia_src_path)/core/SkPath.cpp',
         '<(skia_src_path)/core/SkPathEffect.cpp',
         '<(skia_src_path)/core/SkPathHeap.cpp',