[LayoutNG] Runtime flag for block fragmentation.

Add a LayoutNGBlockFragmentation flag (which implies LayoutNG). Not
enabled by default. When enabled, we will use NG's current block
fragmentation implementation (which is incomplete). When disabled, we'll
fall back to legacy layout for anything that needs block fragmentation.

This flag is deliberately not enabled on the layout_ng trybot, so now a
bunch of multicol / pagination / printing tests will start to pass
there.

In order to retain test coverage for NG's block fragmentation
implementation, the plan is to enable this new flag in some virtual
testsuite for fast/multicol/ & co. Will deal with that in a separate CL.

Bug: 824918
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I4053ba291d5086e495c7ceca30118c5379b99840
Reviewed-on: https://chromium-review.googlesource.com/976223Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545681}

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/fast/forms/select/menulist-appearance-rtl-expected.txt

@@ -74,11 +74,11 @@ layer at (8,268) size 784x2 clip at (0,0) size 0x0
 layer at (8,345) size 784x2 clip at (0,0) size 0x0
   LayoutNGBlockFlow {HR} at (0,329) size 784x2 [border: (1px inset #EEEEEE)]
 layer at (8,399) size 784x160
-  LayoutNGBlockFlow {DIV} at (0,383) size 784x160
+  LayoutBlockFlow {DIV} at (0,383) size 784x160
     LayoutMultiColumnSet (anonymous) at (0,0) size 784x160
 layer at (8,399) size 384x320 backgroundClip at (0,0) size 400x559 clip at (0,0) size 400x559
   LayoutMultiColumnFlowThread (anonymous) at (0,0) size 384x320
-    LayoutNGBlockFlow {DIV} at (0,0) size 384x160
+    LayoutBlockFlow {DIV} at (0,0) size 384x160
       LayoutMenuList {SELECT} at (0,0) size 350x22 [bgcolor=#C0C0C0] [border: (1px solid #A9A9A9)]
         LayoutNGBlockFlow (anonymous) at (1,1) size 348x21
           LayoutText (anonymous) at (4,1) size 174x18
@@ -87,12 +87,12 @@ layer at (8,399) size 384x320 backgroundClip at (0,0) size 400x559 clip at (0,0)
             text run at (91,1) width 18: "03"
             text run at (109,1) width 40 RTL: "\x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
             text run at (149,1) width 29: " fifth"
-      LayoutNGBlockFlow {DIV} at (0,22) size 352x18
+      LayoutBlockFlow {DIV} at (0,22) size 352x18
         LayoutText {#text} at (1,1) size 133x15
           text run at (1,1) width 27: "First "
-          text run at (28,1) width 38: ") \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA}"
+          text run at (28,1) width 38 RTL: ") \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA}"
           text run at (66,1) width 14: "03"
-          text run at (80,1) width 28: "\x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
+          text run at (80,1) width 28 RTL: "\x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
           text run at (108,1) width 26: " fifth"
       LayoutMenuList {SELECT} at (0,40) size 350x22 [bgcolor=#C0C0C0] [border: (1px solid #A9A9A9)]
         LayoutNGBlockFlow (anonymous) at (1,1) size 348x21
@@ -102,28 +102,28 @@ layer at (8,399) size 384x320 backgroundClip at (0,0) size 400x559 clip at (0,0)
             text run at (85,1) width 18: "03"
             text run at (103,1) width 44 RTL: " \x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
             text run at (147,1) width 31: "First"
-      LayoutNGBlockFlow {DIV} at (0,62) size 352x18
+      LayoutBlockFlow {DIV} at (0,62) size 352x18
         LayoutText {#text} at (1,1) size 133x15
           text run at (1,1) width 23: "fifth"
-          text run at (24,1) width 41: ") \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} "
+          text run at (24,1) width 41 RTL: ") \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} "
           text run at (65,1) width 14: "03"
-          text run at (79,1) width 31: " \x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
+          text run at (79,1) width 31 RTL: " \x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
           text run at (110,1) width 24: "First"
       LayoutMenuList {SELECT} at (0,80) size 350x22 [bgcolor=#C0C0C0] [border: (1px solid #A9A9A9)]
         LayoutNGBlockFlow (anonymous) at (1,1) size 348x21
           LayoutText (anonymous) at (4,1) size 174x18
             text run at (4,1) width 174 LTR override: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
-      LayoutNGBlockFlow {DIV} at (0,102) size 352x18
+      LayoutBlockFlow {DIV} at (0,102) size 352x18
         LayoutText {#text} at (1,1) size 133x15
-          text run at (1,1) width 133: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
+          text run at (1,1) width 133 LTR override: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
       LayoutMenuList {SELECT} at (0,120) size 350x22 [bgcolor=#C0C0C0] [border: (1px solid #A9A9A9)]
         LayoutNGBlockFlow (anonymous) at (1,1) size 348x21
           LayoutText (anonymous) at (4,1) size 174x18
             text run at (4,1) width 174 RTL override: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
-      LayoutNGBlockFlow {DIV} at (0,142) size 352x18
+      LayoutBlockFlow {DIV} at (0,142) size 352x18
         LayoutText {#text} at (1,1) size 133x15
-          text run at (1,1) width 133: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
-    LayoutNGBlockFlow {DIV} at (0,160) size 384x160
+          text run at (1,1) width 133 RTL override: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
+    LayoutBlockFlow {DIV} at (0,160) size 384x160
       LayoutMenuList {SELECT} at (0,0) size 350x22 [bgcolor=#C0C0C0] [border: (1px solid #A9A9A9)]
         LayoutNGBlockFlow (anonymous) at (1,1) size 348x21
           LayoutText (anonymous) at (170,1) size 174x18
@@ -132,12 +132,12 @@ layer at (8,399) size 384x320 backgroundClip at (0,0) size 400x559 clip at (0,0)
             text run at (257,1) width 18: "03"
             text run at (275,1) width 40 RTL: "\x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
             text run at (315,1) width 29: " fifth"
-      LayoutNGBlockFlow {DIV} at (0,22) size 352x18
+      LayoutBlockFlow {DIV} at (0,22) size 352x18
         LayoutText {#text} at (218,1) size 133x15
           text run at (218,1) width 27: "First "
-          text run at (245,1) width 38: ") \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA}"
+          text run at (245,1) width 38 RTL: ") \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA}"
           text run at (283,1) width 14: "03"
-          text run at (297,1) width 28: "\x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
+          text run at (297,1) width 28 RTL: "\x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
           text run at (325,1) width 26: " fifth"
       LayoutMenuList {SELECT} at (0,40) size 350x22 [bgcolor=#C0C0C0] [border: (1px solid #A9A9A9)]
         LayoutNGBlockFlow (anonymous) at (1,1) size 348x21
@@ -147,24 +147,24 @@ layer at (8,399) size 384x320 backgroundClip at (0,0) size 400x559 clip at (0,0)
             text run at (251,1) width 18: "03"
             text run at (269,1) width 44 RTL: " \x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
             text run at (313,1) width 31: "First"
-      LayoutNGBlockFlow {DIV} at (0,62) size 352x18
+      LayoutBlockFlow {DIV} at (0,62) size 352x18
         LayoutText {#text} at (218,1) size 133x15
           text run at (218,1) width 23: "fifth"
-          text run at (241,1) width 41: ") \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} "
+          text run at (241,1) width 41 RTL: ") \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} "
           text run at (282,1) width 14: "03"
-          text run at (296,1) width 31: " \x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
+          text run at (296,1) width 31 RTL: " \x{5E9}\x{5E0}\x{5D9}\x{5D4} ("
           text run at (327,1) width 24: "First"
       LayoutMenuList {SELECT} at (0,80) size 350x22 [bgcolor=#C0C0C0] [border: (1px solid #A9A9A9)]
         LayoutNGBlockFlow (anonymous) at (1,1) size 348x21
           LayoutText (anonymous) at (170,1) size 174x18
             text run at (170,1) width 174 LTR override: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
-      LayoutNGBlockFlow {DIV} at (0,102) size 352x18
+      LayoutBlockFlow {DIV} at (0,102) size 352x18
         LayoutText {#text} at (218,1) size 133x15
-          text run at (218,1) width 133: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
+          text run at (218,1) width 133 LTR override: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
       LayoutMenuList {SELECT} at (0,120) size 350x22 [bgcolor=#C0C0C0] [border: (1px solid #A9A9A9)]
         LayoutNGBlockFlow (anonymous) at (1,1) size 348x21
           LayoutText (anonymous) at (170,1) size 174x18
             text run at (170,1) width 174 RTL override: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
-      LayoutNGBlockFlow {DIV} at (0,142) size 352x18
+      LayoutBlockFlow {DIV} at (0,142) size 352x18
         LayoutText {#text} at (218,1) size 133x15
-          text run at (218,1) width 133: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"
+          text run at (218,1) width 133 RTL override: "First \x{5E9}\x{5E0}\x{5D9}\x{5D4} (03) \x{5E8}\x{5D1}\x{5D9}\x{5E2}\x{5D9}\x{5EA} fifth"

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/fast/multicol/composited-layer-expected.txt

-{
-"layers": [
-{
-"name": "LayoutView #document",
-"bounds": [800, 600],
-"drawsContent": false,
-"backgroundColor": "#FFFFFF"
-},
-{
-"name": "Scrolling Layer",
-"bounds": [800, 600],
-"drawsContent": false
-},
-{
-"name": "Scrolling Contents Layer",
-"bounds": [800, 600],
-"contentsOpaque": true,
-"backgroundColor": "#FFFFFF"
-},
-{
-"name": "LayoutNGBlockFlow DIV id='multicol'",
-"bounds": [200, 100],
-"transform": 1
-}
-],
-"transforms": [
-{
-"id": 1,
-"transform": [
-[1, 0, 0, 0],
-[0, 1, 0, 0],
-[0, 0, 1, 0],
-[8, 8, 0, 1]
-]
-}
-]
-}
-

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/fast/multicol/dynamic/insert-spanner-after-inner-multicol-crash-expected.txt

-Insert a spanner right after an inner multicol container and before column content, splitting an existing column row.
-
-PASS if no crash or assertion failure.
-
- 
-

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/fast/multicol/fixedpos-in-transform-at-column-boundary-expected.txt

-Test that a fixed positioned object inside a transform inside a multicol isn't paginated.
-
-The word "YO" should be seen below, with large letter spacing.
-
-Y
-O
-PASS

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/fast/multicol/nested-after-composited-layer-crash-expected.txt

-PASS if no crash or assertion failure.
-
-

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/fragmentation/block-with-float-and-1-orphaned-line-expected.txt

-First column.
-This cyan block should all be in the first column.Second column.
-PASS

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/fragmentation/single-cell-too-large-for-page-expected.txt

-crbug.com/99124: Table rows shouldn't straddle page boundaries.
-
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-Text
-PASS

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/printing/ellipsis-printing-style-expected.txt

-layer at (0,0) size 800x600
-  LayoutView at (0,0) size 1066x799
-layer at (0,0) size 1066x40 backgroundClip at (0,0) size 800x600 clip at (0,0) size 800x600
-  LayoutNGBlockFlow {HTML} at (0,0) size 1066x40
-    LayoutNGBlockFlow {BODY} at (8,8) size 1050x24
-layer at (8,8) size 168x24
-  LayoutNGBlockFlow {DIV} at (0,0) size 168x24 [color=#FFFFFF] [bgcolor=#000000]
-    LayoutText {#text} at (0,0) size 160x16
-      text run at (0,0) width 144: "This text"
-      text run at (144,0) width 16: "\x{2026}"

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/printing/page-height-zero-expected.txt

-Test that an exception is thrown when attempting to set zero page height
-
-On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
-
-
-PASS internals.numberOfPages(100, 0) threw exception TypeError: Failed to execute 'numberOfPages' on 'Internals': Page width and height must be larger than 0..
-PASS internals.pageNumber(document.body, 100, 0) threw exception TypeError: Failed to execute 'pageNumber' on 'Internals': Page width and height must be larger than 0..
-PASS successfullyParsed is true
-
-TEST COMPLETE
-

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/printing/webgl-repeated-printing-expected.txt

-PASS successfullyParsed is true
-
-TEST COMPLETE
-Snapshot width: 800 height: 600
-Test 0: canvas should be green
-PASS pixel[0] is within 1 of 0
-PASS pixel[1] is within 1 of 255
-PASS pixel[2] is within 1 of 0
-Snapshot width: 800 height: 600
-Test 1: canvas should be red
-PASS pixel[0] is within 1 of 255
-PASS pixel[1] is within 1 of 0
-PASS pixel[2] is within 1 of 0
-Snapshot width: 800 height: 600
-Test 2: canvas should be blue
-PASS pixel[0] is within 1 of 0
-PASS pixel[1] is within 1 of 0
-PASS pixel[2] is within 1 of 255
-

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/printing/webgl-repeated-printing-preservedrawingbuffer-expected.txt

-PASS successfullyParsed is true
-
-TEST COMPLETE
-Snapshot width: 800 height: 600
-Test 0: canvas should be green
-PASS pixel[0] is within 1 of 0
-PASS pixel[1] is within 1 of 255
-PASS pixel[2] is within 1 of 0
-Snapshot width: 800 height: 600
-Test 1: canvas should be red
-PASS pixel[0] is within 1 of 255
-PASS pixel[1] is within 1 of 0
-PASS pixel[2] is within 1 of 0
-Snapshot width: 800 height: 600
-Test 2: canvas should be blue
-PASS pixel[0] is within 1 of 0
-PASS pixel[1] is within 1 of 0
-PASS pixel[2] is within 1 of 255
-

third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp

@@ -667,22 +667,34 @@ void StyleAdjuster::AdjustComputedStyle(StyleResolverState& state,
     }
   }
 
-  if (RuntimeEnabledFeatures::LayoutNGEnabled() && !style.ForceLegacyLayout()) {
-    // Form controls are not supported yet.
-    if (element && element->ShouldForceLegacyLayout()) {
+  if (RuntimeEnabledFeatures::LayoutNGEnabled() && !style.ForceLegacyLayout() &&
+      element) {
+    const Document& document = element->GetDocument();
+    if (element->ShouldForceLegacyLayout()) {
+      // Form controls are not supported yet.
       style.SetForceLegacyLayout(true);
-    }
-
-    // TODO(layout-dev): Once LayoutNG handles inline content editable, we
-    // should get rid of following code fragment.
-    else if (style.UserModify() != EUserModify::kReadOnly ||
-             (element && element->GetDocument().InDesignMode())) {
+    } else if (style.UserModify() != EUserModify::kReadOnly ||
+               document.InDesignMode()) {
+      // TODO(layout-dev): Once LayoutNG handles inline content editable, we
+      // should get rid of following code fragment.
       style.SetForceLegacyLayout(true);
 
       if (style.Display() == EDisplay::kInline &&
           parent_style.UserModify() == EUserModify::kReadOnly) {
         style.SetDisplay(EDisplay::kInlineBlock);
       }
+    } else if (!RuntimeEnabledFeatures::LayoutNGBlockFragmentationEnabled()) {
+      // Disable NG for the entire subtree if we're establishing a block
+      // fragmentation context.
+      if (style.SpecifiesColumns() ||
+          (style.IsOverflowPaged() &&
+           element != document.ViewportDefiningElement())) {
+        style.SetForceLegacyLayout(true);
+      } else if (document.Paginated()) {
+        // This needs to be discovered on the root element.
+        DCHECK_EQ(element, document.documentElement());
+        style.SetForceLegacyLayout(true);
+      }
     }
   }
 

third_party/WebKit/Source/core/layout/ng/ng_column_layout_algorithm_test.cc

@@ -16,6 +16,14 @@ class NGColumnLayoutAlgorithmTest : public NGBaseLayoutAlgorithmTest {
   void SetUp() override {
     NGBaseLayoutAlgorithmTest::SetUp();
     style_ = ComputedStyle::Create();
+    was_block_fragmentation_enabled_ =
+        RuntimeEnabledFeatures::LayoutNGBlockFragmentationEnabled();
+    RuntimeEnabledFeatures::SetLayoutNGBlockFragmentationEnabled(true);
+  }
+
+  void TearDown() override {
+    RuntimeEnabledFeatures::SetLayoutNGBlockFragmentationEnabled(
+        was_block_fragmentation_enabled_);
   }
 
   scoped_refptr<NGPhysicalBoxFragment> RunBlockLayoutAlgorithm(
@@ -52,6 +60,7 @@ class NGColumnLayoutAlgorithmTest : public NGBaseLayoutAlgorithmTest {
   }
 
   scoped_refptr<ComputedStyle> style_;
+  bool was_block_fragmentation_enabled_ = false;
 };
 
 TEST_F(NGColumnLayoutAlgorithmTest, EmptyMulticol) {

third_party/WebKit/Source/platform/runtime_enabled_features.json5

@@ -590,6 +590,10 @@
     },
     {
       name: "LayoutNG",
+      implied_by: ["LayoutNGBlockFragmentation"],
+    },
+    {
+      name: "LayoutNGBlockFragmentation",
     },
     {
       name: "LayoutNGFragmentCaching",