Fix under-invalidation of media buffered ranges

third_party/WebKit/Source/core/paint/MediaControlsPainter.cpp

Index: third_party/WebKit/Source/core/paint/MediaControlsPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/MediaControlsPainter.cpp b/third_party/WebKit/Source/core/paint/MediaControlsPainter.cpp
index 827389b4b94b143b7d0724e0a2ba353bf814f0e6..6c6ae44f59a241eb5e0ab5479b27c24650474c64 100644
--- a/third_party/WebKit/Source/core/paint/MediaControlsPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/MediaControlsPainter.cpp
@@ -31,6 +31,7 @@
 #include "core/html/HTMLMediaElement.h"
 #include "core/html/TimeRanges.h"
 #include "core/html/shadow/MediaControlElementTypes.h"
+#include "core/html/shadow/MediaControls.h"
 #include "core/paint/PaintInfo.h"
 #include "core/style/ComputedStyle.h"
 #include "platform/graphics/Gradient.h"
@@ -325,9 +326,12 @@ void MediaControlsPainter::paintMediaSliderInternal(const LayoutObject& object,
 
     paintRoundedSliderBackground(rect, style, context, sliderBackgroundColor);
 
+    TimeRanges* bufferedTimeRanges = mediaElement->mediaControls()->bufferedRangesForPainting();

[liberato (no reviews please), 2016/08/29 15:25:34]

could one use mediaElement->buffered() here as well?  the buffered copy could be
half a second stale.

or, am i just missing something subtle (or obvious :) )?

[Xianzhu, 2016/08/29 18:04:14]

This is required in the under-invalidation checking mode (for testing only) if
we enable caching of MediaSliderPart. In the mode, we force repainting any
object even it's not invalidated, and any changed painting must have been
invalidated. Using buffered() here will break the requirement.

However, using buffered() won't cause any real problem because in we only
repaint an object when it's invalidated.

Reverted changes in this file, and disable caching in under-invalidation
checking mode instead. 

+    if (!bufferedTimeRanges)
+        return;
+
     // Draw the buffered range. Since the element may have multiple buffered ranges and it'd be
     // distracting/'busy' to show all of them, show only the buffered range containing the current play head.
-    TimeRanges* bufferedTimeRanges = mediaElement->buffered();
     float duration = mediaElement->duration();
     float currentTime = mediaElement->currentTime();
     if (std::isnan(duration) || std::isinf(duration) || !duration || std::isnan(currentTime))