Turn on MPD threading in nanobench.

Seems okay after this small patch to skip lockPixels() / unlockPixels().

BUG=skia:3149

CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu13.10-GCE-NoGPU-x86_64-Release-TSAN-Trybot

Review URL: https://codereview.chromium.org/773203003

2 files changed, 4 insertions, 5 deletions

diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index b7603bf3bc..03fabc44f1 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -600,8 +600,7 @@ int nanobench_main();
 int nanobench_main() {
     SetupCrashHandler();
     SkAutoGraphics ag;
-    // Multithreading is disabled pending resolution of skia:3149
-    //SkTaskGroup::Enabler enabled;
+    SkTaskGroup::Enabler enabled;
 
 #if SK_SUPPORT_GPU
     GrContext::Options grContextOpts;
diff --git a/src/core/SkBitmapProcShader.cpp b/src/core/SkBitmapProcShader.cpp
index f01d559058..2e42ef1b9a 100644
--- a/src/core/SkBitmapProcShader.cpp
+++ b/src/core/SkBitmapProcShader.cpp
@@ -92,9 +92,9 @@ static bool valid_for_drawing(const SkBitmap& bm) {
         return false;   // no pixels to read
     }
     if (kIndex_8_SkColorType == bm.colorType()) {
-        // ugh, I have to lock-pixels to inspect the colortable
-        SkAutoLockPixels alp(bm);
-        if (!bm.getColorTable()) {
+        SkBitmap copy(bm);          // Locking and unlocking pixels is not thread safe,
+        SkAutoLockPixels alp(copy); // but we need to call it before getColorTable() is safe.
+        if (!copy.getColorTable()) {
             return false;
         }
     }