Let DM work without a GPU.

dm/DMGpuSupport.h

+#ifndef DMGpuSupport_DEFINED
+#define DMGpuSupport_DEFINED
+
+// Provides Ganesh to DM,
+// or if it's not available, fakes it enough so most code doesn't have to know that.
+
+#include "SkSurface.h"
+
+#if SK_SUPPORT_GPU
+
+// Ganesh is available.  Yippee!
+
+#  include "GrContext.h"
+#  include "GrContextFactory.h"
+
+namespace DM {
+
+static const bool kGPUDisabled = false;
+
+static inline SkSurface* NewGpuSurface(GrContextFactory* grFactory,
+                                       GrContextFactory::GLContextType type,
+                                       SkImageInfo info,
+                                       int samples) {
+    return SkSurface::NewRenderTarget(grFactory->get(type), info, samples);
+}
+
+}  // namespace DM
+
+#else// !SK_SUPPORT_GPU
+
+// Ganesh is not available.  Fake it.
+
+class GrContextFactory {
+public:
+    typedef int GLContextType;
+
+    static const GLContextType kANGLE_GLContextType  = 0,
+                               kDebug_GLContextType  = 0,
+                               kMESA_GLContextType   = 0,
+                               kNVPR_GLContextType   = 0,
+                               kNative_GLContextType = 0,
+                               kNull_GLContextType   = 0;
+};
+
+namespace DM {
+
+static const bool kGPUDisabled = true;
+
+static inline SkSurface* NewGpuSurface(GrContextFactory*,
+                                       GrContextFactory::GLContextType,
+                                       SkImageInfo,
+                                       int) {
+    return NULL;
+}
+
+}  // namespace DM
+
+#endif//SK_SUPPORT_GPU
+
+#endif//DMGpuSupport_DEFINED