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/ChecksumBench.cpp b/bench/ChecksumBench.cpp
index 898c411..7d3ec9f 100644
--- a/bench/ChecksumBench.cpp
+++ b/bench/ChecksumBench.cpp
@@ -4,7 +4,7 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
-#include "SkBenchmark.h"
+#include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkChecksum.h"
 #include "SkMD5.h"
@@ -19,7 +19,7 @@
     kMurmur3_ChecksumType,
 };
 
-class ComputeChecksumBench : public SkBenchmark {
+class ComputeChecksumBench : public Benchmark {
     enum {
         U32COUNT  = 256,
         SIZE      = U32COUNT * 4,
@@ -86,7 +86,7 @@
     }
 
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////