add src-rect-constraint to drawImageRect

Follow-on work
- unify around SrcRectConstraint (i.e. drawBitmapRect)
- remove silly drawBitmapRectToRect alias
- clean-up (possibly remove) alias problems around drawBitmapRect + IRect parameter

BUG=skia:

Review URL: https://codereview.chromium.org/1228083004
diff --git a/src/gpu/SkGpuDevice.h b/src/gpu/SkGpuDevice.h
index 8650765..ec3bfbd 100644
--- a/src/gpu/SkGpuDevice.h
+++ b/src/gpu/SkGpuDevice.h
@@ -96,7 +96,7 @@
     virtual void drawBitmapRect(const SkDraw&, const SkBitmap&,
                                 const SkRect* srcOrNull, const SkRect& dst,
                                 const SkPaint& paint,
-                                SkCanvas::DrawBitmapRectFlags flags) override;
+                                SK_VIRTUAL_CONSTRAINT_TYPE) override;
     virtual void drawSprite(const SkDraw&, const SkBitmap& bitmap,
                             int x, int y, const SkPaint& paint) override;
     virtual void drawText(const SkDraw&, const void* text, size_t len,
@@ -117,7 +117,7 @@
                             const SkPaint&) override;
     void drawImage(const SkDraw&, const SkImage*, SkScalar x, SkScalar y, const SkPaint&) override;
     void drawImageRect(const SkDraw&, const SkImage*, const SkRect* src, const SkRect& dst,
-                       const SkPaint&) override;
+                       const SkPaint&, SkCanvas::SrcRectConstraint) override;
 
     void flush() override;
 
@@ -187,7 +187,7 @@
                           const SkRect* srcRectPtr,
                           const SkSize* dstSizePtr,      // ignored iff srcRectPtr == NULL
                           const SkPaint&,
-                          SkCanvas::DrawBitmapRectFlags flags);
+                          SkCanvas::SrcRectConstraint);
 
     /**
      * Helper functions called by drawBitmapCommon. By the time these are called the SkDraw's
@@ -207,7 +207,7 @@
                             const SkRect&,
                             const GrTextureParams& params,
                             const SkPaint& paint,
-                            SkCanvas::DrawBitmapRectFlags flags,
+                            SkCanvas::SrcRectConstraint,
                             bool bicubic,
                             bool needsTextureDomain);
     void drawTiledBitmap(const SkBitmap& bitmap,
@@ -216,7 +216,7 @@
                          const SkIRect& clippedSrcRect,
                          const GrTextureParams& params,
                          const SkPaint& paint,
-                         SkCanvas::DrawBitmapRectFlags flags,
+                         SkCanvas::SrcRectConstraint,
                          int tileSize,
                          bool bicubic);