DM: write failed comparison mode .pngs one more level deep in the tree.

E.g.  instead of having to compare
    /tmp/dm/565/optimizations.png
vs.
    /tmp/dm/replay/optimizations_565.png

it's now

    /tmp/dm/565/optimizations.png
vs.
    /tmp/dm/replay/565/optimizations.png

This lets working with skdiff go a lot more smoothly.

BUG=
R=bsalomon@google.com

Review URL: https://codereview.chromium.org/88773002

git-svn-id: http://skia.googlecode.com/svn/trunk@12402 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/dm/DMTask.cpp b/dm/DMTask.cpp
index ba74a5f..a5c75f0 100644
--- a/dm/DMTask.cpp
+++ b/dm/DMTask.cpp
@@ -8,14 +8,15 @@
 namespace DM {
 
 Task::Task(Reporter* reporter, TaskRunner* taskRunner)
-    : fReporter(reporter), fTaskRunner(taskRunner) {
+    : fReporter(reporter), fTaskRunner(taskRunner), fDepth(0) {
     fReporter->start();
 }
 
-Task::Task(const Task& that)
-    : INHERITED(that)
-    , fReporter(that.fReporter)
-    , fTaskRunner(that.fTaskRunner) {
+Task::Task(const Task& parent)
+    : INHERITED(parent)
+    , fReporter(parent.fReporter)
+    , fTaskRunner(parent.fTaskRunner)
+    , fDepth(parent.depth()+1) {
     fReporter->start();
 }