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/tests/DataRefTest.cpp b/tests/DataRefTest.cpp
index adb05f9..6a58c16 100644
--- a/tests/DataRefTest.cpp
+++ b/tests/DataRefTest.cpp
@@ -179,7 +179,7 @@
         return;
     }
 
-    SkString path = SkOSPath::SkPathJoin(tmpDir.c_str(), "data_test");
+    SkString path = SkOSPath::Join(tmpDir.c_str(), "data_test");
 
     const char s[] = "abcdefghijklmnopqrstuvwxyz";
     {