Fix CodecSubset benches seg faults for kIndex8

bench/subset/SubsetTranslateBench.cpp

Index: bench/subset/SubsetTranslateBench.cpp
diff --git a/bench/subset/SubsetTranslateBench.cpp b/bench/subset/SubsetTranslateBench.cpp
index 620b6f4903b8da291ee0c8eb34809385825fb188..182969d9a2d07700f409e40a75e135f0099abb90 100644
--- a/bench/subset/SubsetTranslateBench.cpp
+++ b/bench/subset/SubsetTranslateBench.cpp
@@ -55,7 +55,7 @@ bool SubsetTranslateBench::isSuitableFor(Backend backend) {
 void SubsetTranslateBench::onDraw(const int n, SkCanvas* canvas) {
     // When the color type is kIndex8, we will need to store the color table.  If it is
     // used, it will be initialized by the codec.
-    int colorCount;
+    int colorCount = 0;

[scroggo, 2015/06/30 16:40:19]

This got left out of patch set 2, but according to
https://codereview.chromium.org/1160953002/diff/140001/bench/nanobench.cpp#ne...,
we need to initialize it?

[msarett, 2015/06/30 18:40:27]

I switched away from this approach because I thought it was confusing and also
probably worse performance (although this is untested and I doubt it really
makes a difference).  But clearly, it's confusing.

My thinking was that colorCount will only be set to a non-zero value on a
kIndex8 decode.  So then when we initialize the color table below:
1) If it is kIndex8 a color table will be allocated normally.
2) If colorCount is still 0, the constructor for SkColorTable essentially does
nothing.

So this is a really confusing way to get rid of an if statement (and always
construct an SkColorTable, even if it is empty).  Probably not a good approach.

You're right, in the normal approach we don't need to initialize colorCount.

     SkPMColor colors[256];
     if (fUseCodec) {
         for (int count = 0; count < n; count++) {
@@ -68,7 +68,8 @@ void SubsetTranslateBench::onDraw(const int n, SkCanvas* canvas) {
             SkBitmap bitmap;
             // Note that we use the same bitmap for all of the subsets.
             // It might be larger than necessary for the end subsets.
-            bitmap.allocPixels(info.makeWH(fSubsetWidth, fSubsetHeight));
+            bitmap.allocPixels(info.makeWH(fSubsetWidth, fSubsetHeight), NULL,
+                    SkNEW_ARGS(SkColorTable, (colors, colorCount)));
 
             for (int x = 0; x < info.width(); x += fSubsetWidth) {
                 for (int y = 0; y < info.height(); y += fSubsetHeight) {