Use PathFilterGroup in LogServlet

PathFilterGroup has some short-circuiting behavior that PathFilter
does not. This cuts time for log of Chromium's
chrome/browser/chrome_browser_main.cc from 12s to 8s on my
workstation.

This is low-hanging fruit. JGit's log still performs very badly; the
same file logs in under a second with C git.

Change-Id: Ief0f81e87273b95fabe476418cda6b3c5851f449

gitiles-servlet/src/main/java/com/google/gitiles/LogServlet.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/LogServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/LogServlet.java
index e442be5..d904d39 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/LogServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/LogServlet.java
@@ -43,7 +43,7 @@
 import org.eclipse.jgit.revwalk.RevTag;
 import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.treewalk.filter.AndTreeFilter;
-import org.eclipse.jgit.treewalk.filter.PathFilter;
+import org.eclipse.jgit.treewalk.filter.PathFilterGroup;
 import org.eclipse.jgit.treewalk.filter.TreeFilter;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -197,7 +197,7 @@
     }
     if (!Strings.isNullOrEmpty(view.getPathPart())) {
       walk.setTreeFilter(AndTreeFilter.create(
-          PathFilter.create(view.getPathPart()),
+          PathFilterGroup.createFromStrings(view.getPathPart()),
           TreeFilter.ANY_DIFF));
     }
     return walk;