Fix bug in setting directories for tests.

make_canonical_dir_path only worked if the provided directory
did not end with a slash. Remove this function, and call
SkPathJoin instead. Update the documentation to acknowledge
that this is an acceptable use of SkPathJoin, and update its
test.

R=epoger@google.com

Review URL: https://codereview.chromium.org/16098011

git-svn-id: http://skia.googlecode.com/svn/trunk@9458 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/Test.h b/tests/Test.h
index dfa12a6..8cb23c1 100644
--- a/tests/Test.h
+++ b/tests/Test.h
@@ -75,9 +75,9 @@
         bool passed() const { return fPassed; }
         SkMSec elapsedMs() const { return fElapsed; }
 
-        static const SkString& GetTmpDir();
+        static SkString GetTmpDir();
 
-        static const SkString& GetResourcePath();
+        static SkString GetResourcePath();
 
         virtual bool isThreadsafe() const { return true; }