add --dryRun flag to dm

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);
+
 namespace DM {
 
 Task::Task(Reporter* reporter, TaskRunner* taskRunner)
     : fReporter(reporter)
     , fTaskRunner(taskRunner)
     , fDepth(0) {
     fReporter->taskCreated();
 }
 
 Task::Task(const Task& parent)
@@ skipping 26 matching lines @@
 void Task::spawnChildNext(CpuTask* task) {
     fTaskRunner->addNext(task);
 }
 
 CpuTask::CpuTask(Reporter* reporter, TaskRunner* taskRunner) : Task(reporter, taskRunner) {}
 CpuTask::CpuTask(const Task& parent) : Task(parent) {}
 
 void CpuTask::run() {
     if (FLAGS_cpu && !this->shouldSkip()) {
         this->start();
-        this->draw();
+        if (!FLAGS_dryRun) this->draw();
         this->finish();
     }
     SkDELETE(this);
 }
 
 void CpuTask::spawnChild(CpuTask* task) {
     // Run children serially on this (CPU) thread.  This tends to save RAM and is usually no slower.
     // Calling spawnChildNext() is nearly equivalent, but it'd pointlessly contend on the
     // threadpool; spawnChildNext() is most useful when you want to change threadpools.
     task->run();
 }
 
 GpuTask::GpuTask(Reporter* reporter, TaskRunner* taskRunner) : Task(reporter, taskRunner) {}
 
 void GpuTask::run(GrContextFactory& factory) {
     if (FLAGS_gpu && !this->shouldSkip()) {
         this->start();
-        this->draw(&factory);
+        if (!FLAGS_dryRun) this->draw(&factory);
         this->finish();
     }
     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