Store DM failures in an array, not a single string.

dm/DMTestTask.h

 #ifndef DMTestTask_DEFINED
 #define DMTestTask_DEFINED
 
 #include "DMReporter.h"
 #include "DMJsonWriter.h"
 #include "DMTask.h"
 #include "DMTaskRunner.h"
 #include "SkString.h"
 #include "SkTemplates.h"
 #include "Test.h"
 
 // Runs a unit test.
 namespace DM {
 
 class TestReporter : public skiatest::Reporter {
 public:
   TestReporter() {}
 
-  const char* failure() const { return fFailure.c_str(); }
+  const SkTArray<SkString>& failures() const { return fFailures; }
 
 private:
   virtual bool allowExtendedTest() const SK_OVERRIDE;
   virtual bool verbose()           const SK_OVERRIDE;
 
   virtual void onReportFailed(const skiatest::Failure& failure) SK_OVERRIDE {
       JsonWriter::AddTestFailure(failure);
 
       SkString newFailure;
       failure.getFailureString(&newFailure);
-      // TODO: Better to store an array of failures?
-      if (!fFailure.isEmpty()) {
-          fFailure.append("\n\t\t");
-      }
-      fFailure.append(newFailure);
+      fFailures.push_back(newFailure);
   }
 
-  SkString fFailure;
+  SkTArray<SkString> fFailures;
 };
 
 class CpuTestTask : public CpuTask {
 public:
     CpuTestTask(Reporter*, TaskRunner*, skiatest::TestRegistry::Factory);
 
     virtual void draw() SK_OVERRIDE;
     virtual bool shouldSkip() const SK_OVERRIDE { return false; }
     virtual SkString name() const SK_OVERRIDE { return fName; }
 
@@ skipping 13 matching lines @@
 
 private:
     TestReporter fTestReporter;
     SkAutoTDelete<skiatest::Test> fTest;
     const SkString fName;
 };
 
 }  // namespace DM
 
 #endif // DMTestTask_DEFINED