Generate Android.mk for DM.

dm/DMExpectations.h

 #ifndef DMExpectations_DEFINED
 #define DMExpectations_DEFINED
 
 #include "DMTask.h"
 #include "gm_expectations.h"
 
 namespace DM {
 
 struct Expectations {
     virtual ~Expectations() {}
 
     // Return true if bitmap is the correct output for task, else false.
     virtual bool check(const Task& task, SkBitmap bitmap) const = 0;
 };
 
 class NoExpectations : public Expectations {
 public:
     NoExpectations() {}
     bool check(const Task&, SkBitmap) const SK_OVERRIDE { return true; }
 };
 
+#ifdef SK_BUILD_JSON_WRITER
 class JsonExpectations : public Expectations {
 public:
     explicit JsonExpectations(const char* path) : fGMExpectations(path) {}
 
     bool check(const Task& task, SkBitmap bitmap) const SK_OVERRIDE {
         SkString filename = task.name();
         filename.append(".png");
         const skiagm::Expectations expectations = fGMExpectations.get(filename.c_str());
 
         if (expectations.ignoreFailure() || expectations.empty()) {
             return true;
         }
 
         // Delay this calculation as long as possible.  It's expensive.
         const skiagm::GmResultDigest digest(bitmap);
         return expectations.match(digest);
     }
 
 private:
     skiagm::JsonExpectationsSource fGMExpectations;
 };
+#endif
 
 }  // namespace DM
 
 #endif // DMExpectations_DEFINED