Clarify subrect semantics for GrTextureAdjuster and handle mip maps correctly.

src/gpu/GrTextureParamsAdjuster.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrTextureMaker_DEFINED
 #define GrTextureMaker_DEFINED
 
@@ skipping 51 matching lines @@
     /**
     *  If a stretched version of the texture is generated, it may be cached (assuming that
     *  makeCopyKey() returns true). In that case, the maker is notified in case it
     *  wants to note that for when the maker is destroyed.
     */
     virtual void didCacheCopy(const GrUniqueKey& copyKey) = 0;
 
     typedef SkNoncopyable INHERITED;
 };
 
-/** Base class for sources that start out as textures */
+/**
+ * Base class for sources that start out as textures. Optionally allows for a content area subrect.
+ * The intent is not to use content area for subrect rendering. Rather, the pixels outside the
+ * content area have undefined values and shouldn't be read *regardless* of filtering mode or
+ * the SkCanvas::SrcRectConstraint used for subrect draws.
+ */
 class GrTextureAdjuster : public GrTextureProducer {
 public:
     /** Makes the subset of the texture safe to use with the given texture parameters.
         outOffset will be the top-left corner of the subset if a copy is not made. Otherwise,
         the copy will be tight to the contents and outOffset will be (0, 0). If the copy's size
         does not match subset's dimensions then the contents are scaled to fit the copy.*/
     GrTexture* refTextureSafeForParams(const GrTextureParams&, SkIPoint* outOffset);
 
 protected:
-    /** No subset, use the whole texture */
+    /** The whole texture is content. */
     explicit GrTextureAdjuster(GrTexture* original): fOriginal(original) {}
 
-    GrTextureAdjuster(GrTexture* original, const SkIRect& subset);
+    GrTextureAdjuster(GrTexture* original, const SkIRect& contentArea);
 
     GrTexture* originalTexture() { return fOriginal; }
 
-    /** Returns the subset or null for the whole original texture */
-    const SkIRect* subset() { return fSubset.getMaybeNull(); }
+    /** Returns the content area or null for the whole original texture */
+    const SkIRect* contentArea() { return fContentArea.getMaybeNull(); }
 
 private:
-    GrTexture* internalRefTextureSafeForParams(GrTexture*, const SkIRect* subset,
-                                               const GrTextureParams&, SkIPoint* outOffset);
-    SkTLazy<SkIRect>    fSubset;
+    SkTLazy<SkIRect>    fContentArea;
     GrTexture*          fOriginal;
 
     typedef GrTextureProducer INHERITED;
 };
 
 /** 
  * Base class for sources that start out as something other than a texture (encoded image,
  * picture, ...).
  */
 class GrTextureMaker : public GrTextureProducer {
@@ skipping 38 matching lines @@
     virtual GrTexture* generateTextureForParams(GrContext*, const CopyParams&);
 
 private:
     const int fWidth;
     const int fHeight;
 
     typedef GrTextureProducer INHERITED;
 };
 
 #endif