Use target size to scale down a widget preview image

WidgetCells are being recycled in WidgetFullSheet. getWidth/getHeight
could be a recycled dimension. There is also no guarantee that measure
has taken placed before the scale down logic. Let's use the targeted
width for the scale down logic instead.

Test: Manual
Fix: 195417705
Change-Id: Idfb3cc485604d19658e210709bebde6f163003cf

src/com/android/launcher3/widget/WidgetCell.java

@@ -325,10 +325,10 @@ public class WidgetCell extends LinearLayout implements OnLayoutChangeListener {
             return;
         }
         if (drawable != null) {
+            // Scale down the preview size if it's wider than the cell.
             float scale = 1f;
-            if (getWidth() > 0 && getHeight() > 0) {
-                // Scale down the preview size if it's wider than the cell.
-                float maxWidth = getWidth();
+            if (mTargetPreviewWidth > 0) {
+                float maxWidth = mTargetPreviewWidth;
                 float previewWidth = drawable.getIntrinsicWidth() * mPreviewContainerScale;
                 scale = Math.min(maxWidth / previewWidth, 1);
             }