[Paint Preview] Fix positioning on Android M and earlier

Found out that setMatrix() is broken, but concat() is a viable
alternative.

https://stackoverflow.com/questions/17100355/canvas-is-offset-by-setting-identity-matrix-in-ondraw-of-custom-view

Bug: 1126541
Change-Id: I30f4e37dd488385c2f024ac9ae8aa0de8277aa6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461214Reviewed-by: Mehran Mahmoudi <mahmoudi@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815354}

components/paint_preview/player/android/java/src/org/chromium/components/paintpreview/player/frame/PlayerFrameView.java

@@ -98,7 +98,7 @@ class PlayerFrameView extends FrameLayout {
     @Override
     protected void onDraw(Canvas canvas) {
         canvas.save();
-        if (!mScaleMatrix.isIdentity()) canvas.setMatrix(mScaleMatrix);
+        canvas.concat(mScaleMatrix);
         mBitmapPainter.onDraw(canvas);
         canvas.restore();
     }