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/RegionBench.cpp b/bench/RegionBench.cpp
index 21c10af..b3722d4 100644
--- a/bench/RegionBench.cpp
+++ b/bench/RegionBench.cpp
@@ -5,7 +5,7 @@
  * 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 "SkRandom.h"
 #include "SkRegion.h"
 #include "SkString.h"
@@ -67,7 +67,7 @@
     return true;
 }
 
-class RegionBench : public SkBenchmark {
+class RegionBench : public Benchmark {
 public:
     typedef bool (*Proc)(SkRegion& a, SkRegion& b);
 
@@ -114,10 +114,10 @@
     }
 
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
-class RectSectBench : public SkBenchmark {
+class RectSectBench : public Benchmark {
     enum {
         N = 1000
     };
@@ -167,7 +167,7 @@
     }
 
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////