Make SkColorTable explicitly thread-safe.

src/core/SkBitmap.cpp

Index: src/core/SkBitmap.cpp
diff --git a/src/core/SkBitmap.cpp b/src/core/SkBitmap.cpp
index d644ecb12595400777b1479c59b68c88277614d3..c1add1fed95e8c21d3bf1da63cce9ea6d8a6c547 100644
--- a/src/core/SkBitmap.cpp
+++ b/src/core/SkBitmap.cpp
@@ -938,8 +938,7 @@ bool SkBitmap::copyTo(SkBitmap* dst, SkColorType dstColorType, Allocator* alloc)
     // allocate colortable if srcConfig == kIndex8_Config
     SkAutoTUnref<SkColorTable> ctable;
     if (dstColorType == kIndex_8_SkColorType) {
-        // TODO: can we just ref() the src colortable? Is it reentrant-safe?
-        ctable.reset(SkNEW_ARGS(SkColorTable, (*src->getColorTable())));
+        ctable.reset(SkRef(src->getColorTable()));
     }
     if (!tmpDst.tryAllocPixels(alloc, ctable)) {
         return false;