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/ChromeBench.cpp b/bench/ChromeBench.cpp
index b2fc185..4938785 100644
--- a/bench/ChromeBench.cpp
+++ b/bench/ChromeBench.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 "SkPaint.h"
 #include "SkString.h"
@@ -449,7 +449,7 @@
 };
 
 /// Emulates the mix of rects blitted by gmail during scrolling
-class ScrollGmailBench : public SkBenchmark {
+class ScrollGmailBench : public Benchmark {
     enum {
         W = 1254,
         H = 1160,
@@ -488,7 +488,7 @@
 
 
 private:
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 // Disabled this benchmark: it takes 15x longer than any other benchmark