[SPv175] Support incremental invalidation on scrolling contents layer

When the scrolling contents layer is resized and it paints the
background, we should invalidate the expanded/shrunk part of the
background. For SPv1 this is done by calling IncrementallyInvalidatePaint.
For SPv175 we need to pass kIncremental reason to PaintController.

Bug: 732611
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I501ed3e899282b31f4f9d461e23637ab1ca4460d
Reviewed-on: https://chromium-review.googlesource.com/749283Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513221}

third_party/WebKit/LayoutTests/flag-specific/enable-slimming-paint-v175/paint/invalidation/compositing/background-attachment-local-composited-expected.txt

+{
+  "layers": [
+    {
+      "name": "LayoutView #document",
+      "bounds": [800, 600],
+      "contentsOpaque": true,
+      "backgroundColor": "#FFFFFF"
+    },
+    {
+      "name": "LayoutBlockFlow DIV id='container'",
+      "position": [8, 8],
+      "bounds": [400, 400],
+      "backgroundColor": "#0000FF"
+    },
+    {
+      "name": "Scrolling Layer",
+      "position": [8, 8],
+      "bounds": [400, 400],
+      "drawsContent": false
+    },
+    {
+      "name": "Scrolling Contents Layer",
+      "position": [8, 8],
+      "bounds": [400, 2000],
+      "contentsOpaque": true,
+      "backgroundColor": "#0000FF",
+      "paintInvalidations": [
+        {
+          "object": "Scrolling Contents Layer",
+          "rect": [0, 500, 400, 1500],
+          "reason": "incremental"
+        }
+      ],
+      "transform": 1
+    },
+    {
+      "name": "Overflow Controls Host Layer",
+      "position": [8, 8],
+      "bounds": [400, 400],
+      "drawsContent": false
+    },
+    {
+      "name": "Horizontal Scrollbar Layer",
+      "position": [8, 408],
+      "bounds": [400, 0]
+    },
+    {
+      "name": "Vertical Scrollbar Layer",
+      "position": [408, 8],
+      "bounds": [0, 400]
+    }
+  ],
+  "transforms": [
+    {
+      "id": 1,
+      "transform": [
+        [1, 0, 0, 0],
+        [0, 1, 0, 0],
+        [0, 0, 1, 0],
+        [0, -1600, 0, 1]
+      ],
+      "flattenInheritedTransform": false
+    }
+  ],
+  "objectPaintInvalidations": [
+    {
+      "object": "Scrolling Contents Layer",
+      "reason": "incremental"
+    }
+  ]
+}
+

third_party/WebKit/LayoutTests/flag-specific/enable-slimming-paint-v175/paint/invalidation/compositing/background-attachment-local-equivalent-expected.txt

+{
+  "layers": [
+    {
+      "name": "LayoutView #document",
+      "bounds": [800, 600],
+      "contentsOpaque": true,
+      "backgroundColor": "#FFFFFF"
+    },
+    {
+      "name": "LayoutBlockFlow DIV id='container'",
+      "position": [8, 8],
+      "bounds": [400, 400],
+      "backgroundColor": "#0000FF"
+    },
+    {
+      "name": "Scrolling Layer",
+      "position": [8, 8],
+      "bounds": [400, 400],
+      "drawsContent": false
+    },
+    {
+      "name": "Scrolling Contents Layer",
+      "position": [8, 8],
+      "bounds": [400, 2000],
+      "contentsOpaque": true,
+      "backgroundColor": "#0000FF",
+      "paintInvalidations": [
+        {
+          "object": "Scrolling Contents Layer",
+          "rect": [0, 500, 400, 1500],
+          "reason": "incremental"
+        }
+      ],
+      "transform": 1
+    },
+    {
+      "name": "Overflow Controls Host Layer",
+      "position": [8, 8],
+      "bounds": [400, 400],
+      "drawsContent": false
+    },
+    {
+      "name": "Horizontal Scrollbar Layer",
+      "position": [8, 408],
+      "bounds": [400, 0]
+    },
+    {
+      "name": "Vertical Scrollbar Layer",
+      "position": [408, 8],
+      "bounds": [0, 400]
+    }
+  ],
+  "transforms": [
+    {
+      "id": 1,
+      "transform": [
+        [1, 0, 0, 0],
+        [0, 1, 0, 0],
+        [0, 0, 1, 0],
+        [0, -1600, 0, 1]
+      ],
+      "flattenInheritedTransform": false
+    }
+  ],
+  "objectPaintInvalidations": [
+    {
+      "object": "Scrolling Contents Layer",
+      "reason": "incremental"
+    }
+  ]
+}
+

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

@@ -227,35 +227,38 @@ BoxPaintInvalidator::ComputeBackgroundInvalidation() {
 }
 
 void BoxPaintInvalidator::InvalidateScrollingContentsBackground(
-    BackgroundInvalidationType backgroundInvalidationType) {
+    BackgroundInvalidationType background_invalidation_type) {
   if (!BackgroundPaintsOntoScrollingContentsLayer())
     return;
-  if (backgroundInvalidationType == BackgroundInvalidationType::kNone)
+  if (background_invalidation_type == BackgroundInvalidationType::kNone)
     return;
 
-  // TODO(crbug.com/732611): Implement raster invalidation of background on
-  // scrolling contents layer for SPv175.
-  if (!RuntimeEnabledFeatures::SlimmingPaintV175Enabled()) {
+  PaintInvalidationReason reason;
+  if (RuntimeEnabledFeatures::SlimmingPaintV175Enabled()) {
+    reason = background_invalidation_type == BackgroundInvalidationType::kFull
+                 ? PaintInvalidationReason::kBackgroundOnScrollingContentsLayer
+                 : PaintInvalidationReason::kIncremental;
+  } else {
+    // For SPv1 we need this reason for both full and incremental invalidation
+    // to let ObjectPaintInvalidator::SetBackingNeedsPaintInvalidationInRect()
+    // know we are invalidating on the scrolling contents backing.
+    reason = PaintInvalidationReason::kBackgroundOnScrollingContentsLayer;
     const LayoutRect& old_layout_overflow = box_.PreviousLayoutOverflowRect();
     LayoutRect new_layout_overflow = box_.LayoutOverflowRect();
-    if (backgroundInvalidationType == BackgroundInvalidationType::kFull) {
+    if (background_invalidation_type == BackgroundInvalidationType::kFull) {
       ObjectPaintInvalidatorWithContext(box_, context_)
-          .FullyInvalidatePaint(
-              PaintInvalidationReason::kBackgroundOnScrollingContentsLayer,
-              old_layout_overflow, new_layout_overflow);
+          .FullyInvalidatePaint(reason, old_layout_overflow,
+                                new_layout_overflow);
     } else {
-      IncrementallyInvalidatePaint(
-          PaintInvalidationReason::kBackgroundOnScrollingContentsLayer,
-          old_layout_overflow, new_layout_overflow);
+      IncrementallyInvalidatePaint(reason, old_layout_overflow,
+                                   new_layout_overflow);
     }
   }
 
   context_.painting_layer->SetNeedsRepaint();
-  // Currently we use CompositedLayerMapping as the DisplayItemClient to paint
-  // background on the scrolling contents layer.
   ObjectPaintInvalidator(box_).InvalidateDisplayItemClient(
       *box_.Layer()->GetCompositedLayerMapping()->ScrollingContentsLayer(),
-      PaintInvalidationReason::kBackgroundOnScrollingContentsLayer);
+      reason);
 }
 
 PaintInvalidationReason BoxPaintInvalidator::InvalidatePaint() {