[OT-PW] Fix a crash in DrawImageRectOp::RasterWithFlags

It appears that most of the crash in off-thread paint worklet is due
to the paint_record is null in the ImageProvider::ScopedResult. The
reason is that at PaintWorkletImageCache::PaintImageInTask, the Record
from painter_->Paint could be null because the Paint function eventually
calls CSSPaintDefinition::Paint and that could return nullptr.

This CL ensures that all the entries in the records_ have non-null
PaintRecord.

Bug: 957458
Change-Id: I6ce22d3c754cc3daac4c8285554cfaecf2eb654d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1588360
Commit-Queue: Xida Chen <xidachen@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656356}

cc/paint/paint_op_buffer.cc

@@ -1219,6 +1219,7 @@ void DrawImageOp::RasterWithFlags(const DrawImageOp* op,
     DCHECK(IsScaleAdjustmentIdentity(op->scale_adjustment));
     SkAutoCanvasRestore save_restore(canvas, true);
     canvas->translate(op->left, op->top);
+    DCHECK(result && result.paint_record());
     result.paint_record()->Playback(canvas, params);
     return;
   }
@@ -1277,6 +1278,7 @@ void DrawImageRectOp::RasterWithFlags(const DrawImageRectOp* op,
     canvas->concat(
         SkMatrix::MakeRectToRect(op->src, op->dst, SkMatrix::kFill_ScaleToFit));
     canvas->clipRect(op->src);
+    DCHECK(result && result.paint_record());
     result.paint_record()->Playback(canvas, params);
     return;
   }

cc/tiles/paint_worklet_image_cache.cc

@@ -74,6 +74,8 @@ void PaintWorkletImageCache::PaintImageInTask(const PaintImage& paint_image) {
   // matches the PaintGeneratedImage::Draw.
   sk_sp<PaintRecord> record =
       painter_->Paint(paint_image.paint_worklet_input());
+  if (!record)
+    return;
   {
     base::AutoLock hold(records_lock_);
     // It is possible for two or more threads to both pass through the first