Improve comments in paint_recorder

TBR=danakj@chromium.org

Change-Id: I1b99bd50cc3d78ede44f5b46ff2ffe10c7dfdadb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1907075
Commit-Queue: Yi Xu <yiyix@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714755}

cc/paint/paint_recorder.h

@@ -30,7 +30,7 @@ class CC_PAINT_EXPORT PaintRecorder {
     return beginRecording(SkRect::MakeWH(width, height));
   }
 
-  // Only valid between between and finish recording.
+  // Only valid while recording.
   ALWAYS_INLINE RecordPaintCanvas* getRecordingCanvas() {
     return canvas_.has_value() ? &canvas_.value() : nullptr;
   }