Clarify subrect semantics for GrTextureAdjuster and handle mip maps correctly.

src/gpu/SkGr.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkGr.h"
 
@@ skipping 328 matching lines @@
 public:
     explicit TextureBitmap_GrTextureAdjuster(const SkBitmap* bmp)
         : INHERITED(bmp->getTexture(), SkIRect::MakeWH(bmp->width(), bmp->height()))
         , fBmp(bmp) {}
 
 private:
     void makeCopyKey(const CopyParams& params, GrUniqueKey* copyKey) override {
         if (fBmp->isVolatile()) {
             return;
         }
-        // The texture subset must represent the whole bitmap. Texture-backed bitmaps don't support
-        // extractSubset(). Therefore, either the bitmap and the teture are the same size or the
-        // subset's dimensions are the bitmap's dimensions.
+        // The content area must represent the whole bitmap. Texture-backed bitmaps don't support
+        // extractSubset(). Therefore, either the bitmap and the texture are the same size or the
+        // content's dimensions are the bitmap's dimensions which is pinned to the upper left
+        // of the texture.
         GrUniqueKey baseKey;
         GrMakeKeyFromImageID(&baseKey, fBmp->getGenerationID(),
                              SkIRect::MakeWH(fBmp->width(), fBmp->height()));
         MakeCopyKeyFromOrigKey(baseKey, params, copyKey);
     }
 
     void didCacheCopy(const GrUniqueKey& copyKey) override {
         install_bmp_key_invalidator(copyKey, fBmp->pixelRef());
     }
 
@@ skipping 321 matching lines @@
             SkErrorInternals::SetError( kInvalidPaint_SkError,
                                         "Sorry, I don't understand the filtering "
                                         "mode you asked for.  Falling back to "
                                         "MIPMaps.");
             textureFilterMode = GrTextureParams::kMipMap_FilterMode;
             break;
 
     }
     return textureFilterMode;
 }