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/ChartBench.cpp b/bench/ChartBench.cpp
index 9dae5b8..f33d2da 100644
--- a/bench/ChartBench.cpp
+++ b/bench/ChartBench.cpp
@@ -5,7 +5,7 @@
  * found in the LICENSE file.
  */
 
-#include "SkBenchmark.h"
+#include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkPaint.h"
 #include "SkRandom.h"
@@ -84,7 +84,7 @@
 
 // A set of scrolling line plots with the area between each plot filled. Stresses out GPU path
 // filling
-class ChartBench : public SkBenchmark {
+class ChartBench : public Benchmark {
 public:
     ChartBench(bool aa) {
         fShift = 0;
@@ -183,7 +183,7 @@
     SkTDArray<SkScalar> fData[kNumGraphs];
     bool                fAA;
 
-    typedef SkBenchmark INHERITED;
+    typedef Benchmark INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////