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/utils/android/SkAndroidSDKCanvas.h b/src/utils/android/SkAndroidSDKCanvas.h
index a54315d..d22931d 100644
--- a/src/utils/android/SkAndroidSDKCanvas.h
+++ b/src/utils/android/SkAndroidSDKCanvas.h
@@ -43,7 +43,7 @@
     void onDrawBitmap(const SkBitmap& bitmap, SkScalar left, SkScalar top,
                       const SkPaint* paint) override;
     void onDrawBitmapRect(const SkBitmap& bitmap, const SkRect* src, const SkRect& dst,
-                          const SkPaint* paint, DrawBitmapRectFlags flags) override;
+                          const SkPaint* paint, SK_VIRTUAL_CONSTRAINT_TYPE) override;
     void onDrawBitmapNine(const SkBitmap& bitmap, const SkIRect& center,
                           const SkRect& dst, const SkPaint* paint) override;
     void onDrawSprite(const SkBitmap& bitmap, int left, int top,