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/skpdiff/skpdiff_util.cpp b/tools/skpdiff/skpdiff_util.cpp
index 983bee2..4a92f5e 100644
--- a/tools/skpdiff/skpdiff_util.cpp
+++ b/tools/skpdiff/skpdiff_util.cpp
@@ -117,7 +117,7 @@
     while ((entry = readdir(dir))) {
         // dirent only gives relative paths, we need to join them to the base path to check if they
         // are directories.
-        SkString joinedPath = SkOSPath::SkPathJoin(path, entry->d_name);
+        SkString joinedPath = SkOSPath::Join(path, entry->d_name);
 
         // We only care about files
         if (!sk_isdir(joinedPath.c_str())) {