Fix a warning building DM using ninja on Mac.

Here is the warning:
../../dm/DMTask.cpp: In copy constructor ‘DM::Task::Task(const DM::Task&)’:
../../dm/DMTask.cpp:17: warning: base class ‘class SkRunnable’ should be explicitly initialized in the copy constructor

Also add an SK_OVERRIDE.

R=mtklein@google.com

Review URL: https://codereview.chromium.org/76903002

git-svn-id: http://skia.googlecode.com/svn/trunk@12317 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/dm/DMTask.cpp b/dm/DMTask.cpp
index 9b463f9..ba74a5f 100644
--- a/dm/DMTask.cpp
+++ b/dm/DMTask.cpp
@@ -12,7 +12,10 @@
     fReporter->start();
 }
 
-Task::Task(const Task& that) : fReporter(that.fReporter), fTaskRunner(that.fTaskRunner) {
+Task::Task(const Task& that)
+    : INHERITED(that)
+    , fReporter(that.fReporter)
+    , fTaskRunner(that.fTaskRunner) {
     fReporter->start();
 }
 
diff --git a/dm/DMTask.h b/dm/DMTask.h
index 744fd6b..5388196 100644
--- a/dm/DMTask.h
+++ b/dm/DMTask.h
@@ -21,7 +21,7 @@
     Task(const Task& that);
     virtual ~Task();
 
-    void run();
+    void run() SK_OVERRIDE;
 
     virtual void draw() = 0;
     virtual bool usesGpu() const = 0;
@@ -36,6 +36,8 @@
     // Both unowned.
     Reporter* fReporter;
     TaskRunner* fTaskRunner;
+
+    typedef SkRunnable INHERITED;
 };
 
 }  // namespace DM