Add benchmark for PremultiplyAlpha and UnpremultiplyAlpha in Skia

BUG=248549
R=tomhudson@chromium.org, bsalomon@chromium.org, reed@google.com, noel@chromium.org, tomhudson@google.com

Author: jun.a.jiang@intel.com

Review URL: https://chromiumcodereview.appspot.com/16654004

git-svn-id: http://skia.googlecode.com/svn/trunk@9569 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/bench.gypi b/gyp/bench.gypi
index 5ae472b..c7f0c11 100644
--- a/gyp/bench.gypi
+++ b/gyp/bench.gypi
@@ -47,6 +47,7 @@
     '../bench/PicturePlaybackBench.cpp',
     '../bench/PictureRecordBench.cpp',
     '../bench/ReadPixBench.cpp',
+    '../bench/PremulAndUnpremulAlphaOpsBench.cpp',
     '../bench/RectBench.cpp',
     '../bench/RectoriBench.cpp',
     '../bench/RefCntBench.cpp',