Cleanup: Rename SkOSPath functions.

Mostly for brevity and matches better with Python:

Python           | Old C++                 | New C++
os.path.join     | SkOSPath::SkPathJoin    | SkOSPath::Join
os.path.basename | SkOSPath::SkBasename    | SkOSPath::Basename

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

Author: tfarina@chromium.org

Review URL: https://codereview.chromium.org/428443002
diff --git a/tools/bench_playback.cpp b/tools/bench_playback.cpp
index 5343191..a4f3a6a 100644
--- a/tools/bench_playback.cpp
+++ b/tools/bench_playback.cpp
@@ -106,7 +106,7 @@
             continue;
         }
 
-        const SkString path = SkOSPath::SkPathJoin(FLAGS_skps[0], filename.c_str());
+        const SkString path = SkOSPath::Join(FLAGS_skps[0], filename.c_str());
 
         SkAutoTUnref<SkStream> stream(SkStream::NewFromFile(path.c_str()));
         if (!stream) {