Update string Split API.

Return a new vector rather than appending to the parameter.

Delimiters are also a string rather than a character. Split on any
character in the string.

Change-Id: I039b332ace5578590df9e7ca0e8fa3db28db30a3
diff --git a/base/logging.cpp b/base/logging.cpp
index 3d6c0c2..5b70c7d 100644
--- a/base/logging.cpp
+++ b/base/logging.cpp
@@ -108,8 +108,7 @@
     return;
   }
 
-  std::vector<std::string> specs;
-  Split(tags, ' ', &specs);
+  std::vector<std::string> specs = Split(tags, " ");
   for (size_t i = 0; i < specs.size(); ++i) {
     // "tag-pattern:[vdiwefs]"
     std::string spec(specs[i]);