Remove image usage type enum. Use GrTextureParams instead.

BUG=skia:

Review URL: https://codereview.chromium.org/1404433002
diff --git a/src/image/SkImage_Generator.cpp b/src/image/SkImage_Generator.cpp
index 5ce552c..3465289 100644
--- a/src/image/SkImage_Generator.cpp
+++ b/src/image/SkImage_Generator.cpp
@@ -27,7 +27,7 @@
     bool isOpaque() const override { return fCache->info().isOpaque(); }
     SkImage* onNewSubset(const SkIRect&) const override;
     bool getROPixels(SkBitmap*) const override;
-    GrTexture* asTextureRef(GrContext*, SkImageUsageType) const override;
+    GrTexture* asTextureRef(GrContext*, const GrTextureParams&) const override;
     bool onIsLazyGenerated() const override { return true; }
 
 private:
@@ -59,8 +59,8 @@
     return fCache->lockAsBitmap(bitmap, this);
 }
 
-GrTexture* SkImage_Generator::asTextureRef(GrContext* ctx, SkImageUsageType usage) const {
-    return fCache->lockAsTexture(ctx, usage, this);
+GrTexture* SkImage_Generator::asTextureRef(GrContext* ctx, const GrTextureParams& params) const {
+    return fCache->lockAsTexture(ctx, params, this);
 }
 
 SkImage* SkImage_Generator::onNewSubset(const SkIRect& subset) const {