Simplify common case for recttorect

Change-Id: I70e295a677b8cac3d578e3cd57472c833af03877
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/354336
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/samplecode/SampleCamera.cpp b/samplecode/SampleCamera.cpp
index abde083..41da126 100644
--- a/samplecode/SampleCamera.cpp
+++ b/samplecode/SampleCamera.cpp
@@ -36,10 +36,8 @@
             if (GetResourceAsBitmap(resource, &bm)) {
                 SkRect src = { 0, 0, SkIntToScalar(bm.width()), SkIntToScalar(bm.height()) };
                 SkRect dst = { -150, -150, 150, 150 };
-                SkMatrix matrix;
-                matrix.setRectToRect(src, dst, SkMatrix::kFill_ScaleToFit);
                 fShaders.push_back(bm.makeShader(SkSamplingOptions(SkFilterMode::kLinear),
-                                                 matrix));
+                                                 SkMatrix::RectToRect(src, dst)));
             }
         }
         this->setBGColor(0xFFDDDDDD);