Add support for using alternative backends (like DirectX) when creating a GrGpu.

src/gpu/GrGpuFactory.cpp

Index: src/gpu/GrGpuFactory.cpp
diff --git a/src/gpu/GrGpuFactory.cpp b/src/gpu/GrGpuFactory.cpp
index 4b09c14e5182ae9e299c073403f5835b3537cec1..74adf98236706662fe04c1582e14276913c007c4 100644
--- a/src/gpu/GrGpuFactory.cpp
+++ b/src/gpu/GrGpuFactory.cpp
@@ -7,37 +7,49 @@
  */
 
 
-#include "GrTypes.h"
+#include "GrGpuFactory.h"
 
 #include "gl/GrGLConfig.h"
 
 #include "GrGpu.h"
 #include "gl/GrGLGpu.h"
 
-GrGpu* GrGpu::Create(GrBackend backend, GrBackendContext backendContext, GrContext* context) {
-
+static GrGpu* gl_gpu_create(GrBackendContext backendContext, GrContext* context) {
     const GrGLInterface* glInterface = NULL;
     SkAutoTUnref<const GrGLInterface> glInterfaceUnref;
 
-    if (kOpenGL_GrBackend == backend) {
-        glInterface = reinterpret_cast<const GrGLInterface*>(backendContext);
-        if (NULL == glInterface) {
-            glInterface = GrGLDefaultInterface();
-            // By calling GrGLDefaultInterface we've taken a ref on the
-            // returned object. We only want to hold that ref until after
-            // the GrGpu is constructed and has taken ownership.
-            glInterfaceUnref.reset(glInterface);
-        }
-        if (NULL == glInterface) {
+    glInterface = reinterpret_cast<const GrGLInterface*>(backendContext);
+    if (NULL == glInterface) {
+        glInterface = GrGLDefaultInterface();
+        // By calling GrGLDefaultInterface we've taken a ref on the
+        // returned object. We only want to hold that ref until after
+        // the GrGpu is constructed and has taken ownership.
+        glInterfaceUnref.reset(glInterface);
+    }
+    if (NULL == glInterface) {
 #ifdef SK_DEBUG
-            SkDebugf("No GL interface provided!\n");
+        SkDebugf("No GL interface provided!\n");
 #endif
-            return NULL;
-        }
-        GrGLContext ctx(glInterface);
-        if (ctx.isInitialized()) {
-            return SkNEW_ARGS(GrGLGpu, (ctx, context));
-        }
+        return NULL;
+    }
+    GrGLContext ctx(glInterface);
+    if (ctx.isInitialized()) {
+        return SkNEW_ARGS(GrGLGpu, (ctx, context));
     }
     return NULL;
 }
+
+static const int kMaxNumBackends = 4;
+static CreateGpuProc gGpuFactories[kMaxNumBackends] = {gl_gpu_create, NULL, NULL, NULL};
+
+GrGpuFactoryRegistrar::GrGpuFactoryRegistrar(int i, CreateGpuProc proc) {
+    gGpuFactories[i] = proc;
+}
+
+GrGpu* GrGpu::Create(GrBackend backend, GrBackendContext backendContext, GrContext* context) {
+    SkASSERT((int)backend < kMaxNumBackends);
+    if (!gGpuFactories[backend]) {
+        return NULL;
+    }
+    return (gGpuFactories[backend])(backendContext, context);
+}