DM: add --writePath

For fun, make the output prettier, hiding ", N failures" unless there is one.

BUG=
R=bsalomon@google.com

Review URL: https://codereview.chromium.org/29293003

git-svn-id: http://skia.googlecode.com/svn/trunk@11867 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/dm/DMReporter.cpp b/dm/DMReporter.cpp
index 7a0c20e..3d9dae5 100644
--- a/dm/DMReporter.cpp
+++ b/dm/DMReporter.cpp
@@ -3,7 +3,13 @@
 namespace DM {
 
 void Reporter::updateStatusLine() const {
-    SkDebugf("\r\033[K%d / %d, %d failed", this->finished(), this->started(), this->failed());
+    SkString status;
+    status.printf("\r\033[K%d / %d", this->finished(), this->started());
+    const int failed = this->failed();
+    if (failed > 0) {
+        status.appendf(", %d failed", failed);
+    }
+    SkDebugf(status.c_str());
 }
 
 int32_t Reporter::failed() const {