Account for writing-mode flip of the composited element for interest rects.

BUG=581264

Review URL: https://codereview.chromium.org/1640363003

Cr-Commit-Position: refs/heads/master@{#372117}

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

@@ -2256,6 +2256,9 @@ IntRect CompositedLayerMapping::recomputeInterestRect(const GraphicsLayer* graph
     // Start with the bounds of the graphics layer in the space of the anchor LayoutObject.
     FloatRect graphicsLayerBoundsInObjectSpace(graphicsLayerBounds);
     graphicsLayerBoundsInObjectSpace.move(offsetFromAnchorLayoutObject);
+    // The object space means including writing mode flip.
+    if (anchorLayoutObject->isBox())
+        toLayoutBox(anchorLayoutObject)->flipForWritingMode(graphicsLayerBoundsInObjectSpace);
 
     // Now map the bounds to its visible content rect in screen space, including applying clips along the way.
     LayoutRect visibleContentRect(graphicsLayerBoundsInObjectSpace);

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp

@@ -109,6 +109,23 @@ TEST_F(CompositedLayerMappingTest, TallLayerWholeDocumentInterestRect)
     EXPECT_RECT_EQ(IntRect(0, 0, 200, 10000), computeInterestRect(paintLayer->compositedLayerMapping(), paintLayer->graphicsLayerBacking(), IntRect()));
 }
 
+TEST_F(CompositedLayerMappingTest, VerticalRightLeftWritingModeDocument)
+{
+    setBodyInnerHTML("<style>html,body { margin: 0px } html { -webkit-writing-mode: vertical-rl}</style> <div id='target' style='width: 10000px; height: 200px;'></div>");
+
+    document().settings()->setMainFrameClipsContent(false);
+
+    document().view()->updateAllLifecyclePhases();
+    document().view()->scrollTo(DoublePoint(-5000, 0));
+    document().view()->updateAllLifecyclePhases();
+
+    PaintLayer* paintLayer = document().layoutView()->layer();
+    ASSERT_TRUE(paintLayer->graphicsLayerBacking());
+    ASSERT_TRUE(paintLayer->compositedLayerMapping());
+    // A scroll by -5000px is equivalent to a scroll by (10000 - 5000 - 800)px = 4200px in non-RTL mode. Expanding
+    // the resulting rect by 4000px in each direction yields this result.
+    EXPECT_RECT_EQ(IntRect(200, 0, 8800, 600), recomputeInterestRect(paintLayer->graphicsLayerBacking()));
+}
 
 TEST_F(CompositedLayerMappingTest, RotatedInterestRect)
 {