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/samplecode/SampleUnpremul.cpp b/samplecode/SampleUnpremul.cpp
index ab99ecb..bfe69e0b 100644
--- a/samplecode/SampleUnpremul.cpp
+++ b/samplecode/SampleUnpremul.cpp
@@ -106,7 +106,7 @@
         }
 
         // Name, size of the file, and whether or not it is premultiplied.
-        SkString header(SkOSPath::SkBasename(fCurrFile.c_str()));
+        SkString header(SkOSPath::Basename(fCurrFile.c_str()));
         header.appendf("     [%dx%d]     %s", fBitmap.width(), fBitmap.height(),
                        (fPremul ? "premultiplied" : "unpremultiplied"));
         canvas->drawText(header.c_str(), header.size(), 0, height, paint);
@@ -167,7 +167,7 @@
                 return;
             }
         }
-        fCurrFile = SkOSPath::SkPathJoin(fResPath.c_str(), basename.c_str());
+        fCurrFile = SkOSPath::Join(fResPath.c_str(), basename.c_str());
         this->decodeCurrFile();
     }