Fix thumbnail disappearing during staged split animation

Previous set the thumbnail view to be visible initially. After deciding not to do so, forgot to put the visibility statement back. Also the transform matrix needs to reset before posting new scales.

Test: https://recall.googleplex.com/projects/f46cfe9c-8076-4efe-bf8a-b1cc4f1f5e1b/sessions/6576df3a-6d14-4b7e-8fb2-1c0a335472e4
Fixes: 194414938
Change-Id: I25fe39ea99943a3c1e2257681df3eb379bc30e51

quickstep/src/com/android/quickstep/views/FloatingTaskThumbnailView.java

@@ -62,6 +62,7 @@ public class FloatingTaskThumbnailView extends View {
 
         // Scale down the bitmap to fix x, and crop in y.
         float scale = 1.0f * getMeasuredWidth() / mBitmap.getWidth();
+        mMatrix.reset();
         mMatrix.postScale(scale, scale);
         mBitmapShader.setLocalMatrix(mMatrix);
 

quickstep/src/com/android/quickstep/views/FloatingTaskView.java

@@ -91,6 +91,8 @@ public class FloatingTaskView extends FrameLayout {
         // Copy bounds of exiting thumbnail into ImageView
         mThumbnailView.setThumbnail(thumbnail);
 
+        mThumbnailView.setVisibility(VISIBLE);
+
         RecentsView recentsView = launcher.getOverviewPanel();
         mOrientationHandler = recentsView.getPagedOrientationHandler();
         mSplitPlaceholderView.setIcon(icon,