SkColorTable locking serves no purpose anymore.

src/images/SkImageDecoder_libpng.cpp

Index: src/images/SkImageDecoder_libpng.cpp
diff --git a/src/images/SkImageDecoder_libpng.cpp b/src/images/SkImageDecoder_libpng.cpp
index 0890eaacaffacf8e4af3af71d38726c493294ba4..8a3e40ea19633b639448d1af73efabcdbd69ec54 100644
--- a/src/images/SkImageDecoder_libpng.cpp
+++ b/src/images/SkImageDecoder_libpng.cpp
@@ -413,8 +413,8 @@ SkImageDecoder::Result SkPNGImageDecoder::onDecode(SkStream* sk_stream, SkBitmap
             even if our decodedBitmap doesn't, due to the request that we
             upscale png's palette to a direct model
          */
-        SkAutoLockColors ctLock(colorTable);
-        if (!sampler.begin(decodedBitmap, sc, *this, ctLock.colors())) {
+        const SkPMColor* colors = colorTable ? colorTable->readColors() : NULL;
+        if (!sampler.begin(decodedBitmap, sc, *this, colors)) {
             return kFailure;
         }
         const int height = decodedBitmap->height();
@@ -894,8 +894,8 @@ bool SkPNGImageDecoder::onDecodeSubset(SkBitmap* bm, const SkIRect& region) {
             even if our decodedBitmap doesn't, due to the request that we
             upscale png's palette to a direct model
          */
-        SkAutoLockColors ctLock(colorTable);
-        if (!sampler.begin(&decodedBitmap, sc, *this, ctLock.colors())) {
+        const SkPMColor* colors = colorTable ? colorTable->readColors() : NULL;
+        if (!sampler.begin(&decodedBitmap, sc, *this, colors)) {
             return false;
         }
         const int height = decodedBitmap.height();
@@ -1047,8 +1047,7 @@ static int computeBitDepth(int colorCount) {
 static inline int pack_palette(SkColorTable* ctable,
                                png_color* SK_RESTRICT palette,
                                png_byte* SK_RESTRICT trans, bool hasAlpha) {
-    SkAutoLockColors alc(ctable);
-    const SkPMColor* SK_RESTRICT colors = alc.colors();
+    const SkPMColor* SK_RESTRICT colors = ctable ? ctable->readColors() : NULL;
     const int ctCount = ctable->count();
     int i, num_trans = 0;