Adding public API method on SkImage for extracting the GPU texture handle.

src/image/SkImage_Gpu.cpp

Index: src/image/SkImage_Gpu.cpp
===================================================================
--- src/image/SkImage_Gpu.cpp	(revision 8915)
+++ src/image/SkImage_Gpu.cpp	(working copy)
@@ -21,6 +21,7 @@
     virtual ~SkImage_Gpu();
 
     virtual void onDraw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*) SK_OVERRIDE;
+    virtual GrTexture* onGetTexture() SK_OVERRIDE;
 
     GrTexture* getTexture() { return fTexture; }
 
@@ -56,6 +57,10 @@
     canvas->drawBitmap(fBitmap, x, y, paint);
 }
 
+GrTexture* SkImage_Gpu::onGetTexture() {
+    return fTexture;
+}
+
 void SkImage_Gpu::setTexture(GrTexture* texture) {
 
     if (texture == fTexture) {