share dm and command flags

dm/DMTask.cpp

 #include "DMTask.h"
 #include "DMTaskRunner.h"
-#include "SkCommandLineFlags.h"
-
-DEFINE_bool(cpu, true, "Master switch for running CPU-bound work.");
-DEFINE_bool(gpu, true, "Master switch for running GPU-bound work.");
-
-DECLARE_bool(dryRun);
+#include "SkCommonFlags.h"
 
 namespace DM {
 
 Task::Task(Reporter* reporter, TaskRunner* taskRunner)
     : fReporter(reporter)
     , fTaskRunner(taskRunner)
     , fDepth(0) {
     fReporter->taskCreated();
 }
 
@@ skipping 58 matching lines @@
     SkDELETE(this);
 }
 
 void GpuTask::spawnChild(CpuTask* task) {
     // Really spawn a new task so it runs on the CPU threadpool instead of the GPU one we're on now.
     // It goes on the front of the queue to minimize the time we must hold reference bitmaps in RAM.
     this->spawnChildNext(task);
 }
 
 }  // namespace DM