Remove Sk prefix from some bench classes.

This idea came while commenting on
https://codereview.chromium.org/343583005/

Since SkBenchmark, SkBenchLogger and SkGMBench are not part of the Skia library,
they should not have the Sk prefix.

BUG=None
TEST=make all
R=mtklein@google.com

Author: tfarina@chromium.org

Review URL: https://codereview.chromium.org/347823004
diff --git a/bench/XfermodeBench.cpp b/bench/XfermodeBench.cpp
index 1910b75..f73943b 100644
--- a/bench/XfermodeBench.cpp
+++ b/bench/XfermodeBench.cpp
@@ -6,7 +6,7 @@
  * found in the LICENSE file.
  */
 
-#include "SkBenchmark.h"
+#include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkPaint.h"
 #include "SkRandom.h"
@@ -14,7 +14,7 @@
 #include "SkXfermode.h"
 
 // Benchmark that draws non-AA rects with an SkXfermode::Mode
-class XfermodeBench : public SkBenchmark {
+class XfermodeBench : public Benchmark {
 public:
     XfermodeBench(SkXfermode::Mode mode) {
         fXfermode.reset(SkXfermode::Create(mode));
@@ -58,10 +58,10 @@
     SkAutoTUnref<SkXfermode> fXfermode;
     SkString fName;
 
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
-class XferCreateBench : public SkBenchmark {
+class XferCreateBench : public Benchmark {
 public:
     virtual bool isSuitableFor(Backend backend) SK_OVERRIDE {
         return backend == kNonRendering_Backend;
@@ -80,7 +80,7 @@
     }
 
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////