Don't remove background when resizing

This leads to flickers, as we should not draw in a translucent way
if we didn't specify that our window is translucent, because the
renderer has some about translucency.

Instead, we should clip the backdrop content by the inverse of the
content clip rect, which is not yet implemented.

Bug: 28009524
Change-Id: Ia3f54fb83997ace863e78ff1cbe45cfb64f92f26

core/java/com/android/internal/policy/DecorView.java

@@ -210,7 +210,6 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
     private Drawable mResizingBackgroundDrawable;
     private Drawable mCaptionBackgroundDrawable;
     private Drawable mUserCaptionBackgroundDrawable;
-    private Drawable mOriginalBackgroundDrawable;
 
     private float mAvailableWidth;
 
@@ -891,11 +890,6 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
                 mBackgroundPadding.setEmpty();
             }
             drawableChanged();
-
-            // Make sure we don't reset to the old drawable when finishing resizing.
-            if (mResizeMode != RESIZE_MODE_INVALID) {
-                mOriginalBackgroundDrawable = null;
-            }
         }
     }
 
@@ -1960,9 +1954,6 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
             updateElevation();
 
             updateColorViews(null /* insets */, false);
-
-            mOriginalBackgroundDrawable = getBackground();
-            setBackgroundDrawable(null);
         }
         mResizeMode = resizeMode;
         getViewRootImpl().requestInvalidateRootRenderNode();
@@ -1974,10 +1965,6 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         updateColorViews(null /* insets */, false);
         mResizeMode = RESIZE_MODE_INVALID;
         getViewRootImpl().requestInvalidateRootRenderNode();
-        if (mOriginalBackgroundDrawable != null) {
-            setBackgroundDrawable(mOriginalBackgroundDrawable);
-            mOriginalBackgroundDrawable = null;
-        }
     }
 
     @Override