Add |contains_only_whitespace_| to LayoutText and TextRun

This CL takes advantage of the loop through text in LayoutText to store
a variable indicating whether text contains only 'whitespace' or not.
The main purpose of the loop is to compute widths but this seems like a
reasonable place to also store this new information, to avoid an extra
iteration over the text.

Now, TextRun has a boolean variable indicating whether the text to be
painted contains a whitespace or not. For now, the boolean is only
changed in InlineTextBox::ConstructTextRun to prevent Font::DrawText
from returning true. The return value of this method is only used to
determine whether SetTextPainted() is called in
GraphicsContext::DrawTextInternal.

PaintController::SetTextPainted is the method that triggers First
Contentful Paint (caused by text) on PaintTiming. We do not want it to
be triggered on trivial whitespace text rendering.

Test: Check whether FCP is observed on a document with just
<div>&nbsp</div>

Also, this fix should allow landing the test in:
https://chromium-review.googlesource.com/c/chromium/src/+/769929

Bug: 785344
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Id219eeaced4679eda9c26acde7fd4fdb0cb1e891
Reviewed-on: https://chromium-review.googlesource.com/786336Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519455}

third_party/WebKit/Source/core/layout/LayoutText.cpp

@@ -66,7 +66,7 @@
 namespace blink {
 
 struct SameSizeAsLayoutText : public LayoutObject {
-  uint32_t bitfields : 16;
+  uint32_t bitfields : 11;
   float widths[4];
   String text;
   void* pointers[2];
@@ -160,6 +160,8 @@ LayoutText::LayoutText(Node* node, scoped_refptr<StringImpl> str)
       lines_dirty_(false),
       contains_reversed_text_(false),
       known_to_have_no_overflow_and_no_fallback_fonts_(false),
+      contains_only_whitespace_or_nbsp_(
+          static_cast<unsigned>(OnlyWhitespaceOrNbsp::kUnknown)),
       min_width_(-1),
       max_width_(-1),
       first_line_min_width_(0),
@@ -1076,6 +1078,8 @@ void LayoutText::ComputePreferredLogicalWidths(
   has_breakable_start_ = false;
   has_breakable_end_ = false;
   has_end_white_space_ = false;
+  contains_only_whitespace_or_nbsp_ =
+      static_cast<unsigned>(OnlyWhitespaceOrNbsp::kYes);
 
   const ComputedStyle& style_to_use = StyleRef();
   const Font& f = style_to_use.GetFont();  // FIXME: This ignores first-line.
@@ -1164,8 +1168,14 @@ void LayoutText::ComputePreferredLogicalWidths(
       } else {
         is_space = true;
       }
+    } else if (c == kSpaceCharacter) {
+      is_space = true;
+    } else if (c == kNoBreakSpaceCharacter) {
+      is_space = false;
     } else {
-      is_space = c == kSpaceCharacter;
+      is_space = false;
+      contains_only_whitespace_or_nbsp_ =
+          static_cast<unsigned>(OnlyWhitespaceOrNbsp::kNo);
     }
 
     bool is_breakable_location =
@@ -1540,6 +1550,12 @@ static inline bool IsInlineFlowOrEmptyText(const LayoutObject* o) {
   return ToLayoutText(o)->GetText().IsEmpty();
 }
 
+OnlyWhitespaceOrNbsp LayoutText::ContainsOnlyWhitespaceOrNbsp() const {
+  return PreferredLogicalWidthsDirty() ? OnlyWhitespaceOrNbsp::kUnknown
+                                       : static_cast<OnlyWhitespaceOrNbsp>(
+                                             contains_only_whitespace_or_nbsp_);
+}
+
 UChar LayoutText::PreviousCharacter() const {
   // find previous text layoutObject if one exists
   const LayoutObject* previous_text = PreviousInPreOrder();

third_party/WebKit/Source/core/layout/LayoutText.h

@@ -38,6 +38,8 @@ class AbstractInlineTextBox;
 class InlineTextBox;
 class NGOffsetMapping;
 
+enum class OnlyWhitespaceOrNbsp : unsigned { kUnknown = 0, kNo = 1, kYes = 2 };
+
 // LayoutText is the root class for anything that represents
 // a text node (see core/dom/Text.h).
 //
@@ -256,6 +258,8 @@ class CORE_EXPORT LayoutText : public LayoutObject {
     known_to_have_no_overflow_and_no_fallback_fonts_ = false;
   }
 
+  OnlyWhitespaceOrNbsp ContainsOnlyWhitespaceOrNbsp() const;
+
   virtual UChar PreviousCharacter() const;
 
  protected:
@@ -330,22 +334,23 @@ class CORE_EXPORT LayoutText : public LayoutObject {
   // We put the bitfield first to minimize padding on 64-bit.
 
   // Whether or not we can be broken into multiple lines.
-  bool has_breakable_char_ : 1;
+  unsigned has_breakable_char_ : 1;
   // Whether or not we have a hard break (e.g., <pre> with '\n').
-  bool has_break_ : 1;
+  unsigned has_break_ : 1;
   // Whether or not we have a variable width tab character (e.g., <pre> with
   // '\t').
-  bool has_tab_ : 1;
-  bool has_breakable_start_ : 1;
-  bool has_breakable_end_ : 1;
-  bool has_end_white_space_ : 1;
+  unsigned has_tab_ : 1;
+  unsigned has_breakable_start_ : 1;
+  unsigned has_breakable_end_ : 1;
+  unsigned has_end_white_space_ : 1;
   // This bit indicates that the text run has already dirtied specific line
   // boxes, and this hint will enable layoutInlineChildren to avoid just
   // dirtying everything when character data is modified (e.g., appended/
   // inserted or removed).
-  bool lines_dirty_ : 1;
-  bool contains_reversed_text_ : 1;
-  mutable bool known_to_have_no_overflow_and_no_fallback_fonts_ : 1;
+  unsigned lines_dirty_ : 1;
+  unsigned contains_reversed_text_ : 1;
+  mutable unsigned known_to_have_no_overflow_and_no_fallback_fonts_ : 1;
+  unsigned contains_only_whitespace_or_nbsp_ : 2;
 
   float min_width_;
   float max_width_;

third_party/WebKit/Source/core/layout/LayoutTextTest.cpp

@@ -121,6 +121,33 @@ TEST_F(LayoutTextTest, WidthLengthBeyondLength) {
   ASSERT_LE(width, 20.f);
 }
 
+TEST_F(LayoutTextTest, ContainsOnlyWhitespaceOrNbsp) {
+  // Note that '&nbsp' is needed when only including whitespace to force
+  // LayoutText creation from the div.
+  SetBasicBody("&nbsp");
+  // GetWidth will also compute |contains_only_whitespace_|.
+  GetBasicText()->Width(0u, 1u, LayoutUnit(), TextDirection::kLtr, false);
+  EXPECT_EQ(OnlyWhitespaceOrNbsp::kYes,
+            GetBasicText()->ContainsOnlyWhitespaceOrNbsp());
+
+  SetBasicBody("   \t\t\n \n\t &nbsp \n\t&nbsp\n \t");
+  EXPECT_EQ(OnlyWhitespaceOrNbsp::kUnknown,
+            GetBasicText()->ContainsOnlyWhitespaceOrNbsp());
+  GetBasicText()->Width(0u, 18u, LayoutUnit(), TextDirection::kLtr, false);
+  EXPECT_EQ(OnlyWhitespaceOrNbsp::kYes,
+            GetBasicText()->ContainsOnlyWhitespaceOrNbsp());
+
+  SetBasicBody("abc");
+  GetBasicText()->Width(0u, 3u, LayoutUnit(), TextDirection::kLtr, false);
+  EXPECT_EQ(OnlyWhitespaceOrNbsp::kNo,
+            GetBasicText()->ContainsOnlyWhitespaceOrNbsp());
+
+  SetBasicBody("  \t&nbsp\nx \n");
+  GetBasicText()->Width(0u, 8u, LayoutUnit(), TextDirection::kLtr, false);
+  EXPECT_EQ(OnlyWhitespaceOrNbsp::kNo,
+            GetBasicText()->ContainsOnlyWhitespaceOrNbsp());
+}
+
 TEST_P(ParameterizedLayoutTextTest, CaretMinMaxOffset) {
   SetBasicBody("foo");
   EXPECT_EQ(0, GetBasicText()->CaretMinOffset());

third_party/WebKit/Source/core/layout/api/LineLayoutText.h

@@ -53,6 +53,10 @@ class LineLayoutText : public LineLayoutItem {
     return ToText()->IsAllCollapsibleWhitespace();
   }
 
+  OnlyWhitespaceOrNbsp ContainsOnlyWhitespaceOrNbsp() const {
+    return ToText()->ContainsOnlyWhitespaceOrNbsp();
+  }
+
   UChar CharacterAt(unsigned offset) const {
     return ToText()->CharacterAt(offset);
   }

third_party/WebKit/Source/core/layout/line/InlineTextBox.cpp

@@ -34,8 +34,10 @@
 #include "core/layout/line/AbstractInlineTextBox.h"
 #include "core/layout/line/EllipsisBox.h"
 #include "core/paint/InlineTextBoxPainter.h"
+#include "core/paint/PaintInfo.h"
 #include "platform/fonts/CharacterRange.h"
 #include "platform/fonts/FontCache.h"
+#include "platform/graphics/paint/PaintController.h"
 #include "platform/wtf/Vector.h"
 #include "platform/wtf/text/StringBuilder.h"
 
@@ -546,6 +548,10 @@ void InlineTextBox::Paint(const PaintInfo& paint_info,
                           LayoutUnit /*lineTop*/,
                           LayoutUnit /*lineBottom*/) const {
   InlineTextBoxPainter(*this).Paint(paint_info, paint_offset);
+  if (GetLineLayoutItem().ContainsOnlyWhitespaceOrNbsp() !=
+      OnlyWhitespaceOrNbsp::kYes) {
+    paint_info.context.GetPaintController().SetTextPainted();
+  }
 }
 
 void InlineTextBox::SelectionStartEnd(int& s_pos, int& e_pos) const {
@@ -597,6 +603,10 @@ void InlineTextBox::PaintTextMatchMarkerForeground(
     const Font& font) const {
   InlineTextBoxPainter(*this).PaintTextMatchMarkerForeground(
       paint_info, box_origin, marker, style, font);
+  if (GetLineLayoutItem().ContainsOnlyWhitespaceOrNbsp() !=
+      OnlyWhitespaceOrNbsp::kYes) {
+    paint_info.context.GetPaintController().SetTextPainted();
+  }
 }
 
 void InlineTextBox::PaintTextMatchMarkerBackground(

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

@@ -69,6 +69,9 @@ void EllipsisBoxPainter::PaintEllipsis(const PaintInfo& paint_info,
                            ellipsis_box_.IsHorizontal());
   text_painter.Paint(0, ellipsis_box_.EllipsisStr().length(),
                      ellipsis_box_.EllipsisStr().length(), text_style);
+  // TODO(npm): Check that there are non-whitespace characters. See
+  // crbug.com/788444.
+  context.GetPaintController().SetTextPainted();
 }
 
 }  // namespace blink

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

@@ -178,6 +178,9 @@ void ListMarkerPainter::Paint(const PaintInfo& paint_info,
     context.DrawText(font, text_run_paint_info,
                      text_origin + IntSize(font.Width(suffix_run), 0));
   }
+  // TODO(npm): Check that there are non-whitespace characters. See
+  // crbug.com/788444.
+  context.GetPaintController().SetTextPainted();
 }
 
 }  // namespace blink

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

@@ -465,6 +465,9 @@ void SVGInlineTextBoxPainter::PaintText(const PaintInfo& paint_info,
                 text_size.Height());
 
   context.DrawText(scaled_font, text_run_paint_info, text_origin, flags);
+  // TODO(npm): Check that there are non-whitespace characters. See
+  // crbug.com/788444.
+  context.GetPaintController().SetTextPainted();
 }
 
 void SVGInlineTextBoxPainter::PaintText(const PaintInfo& paint_info,

third_party/WebKit/Source/core/paint/ng/ng_text_painter.cc

@@ -16,6 +16,7 @@
 #include "platform/fonts/NGTextFragmentPaintInfo.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/GraphicsContextStateSaver.h"
+#include "platform/graphics/paint/PaintController.h"
 #include "platform/wtf/Assertions.h"
 #include "platform/wtf/text/CharacterNames.h"
 
@@ -56,6 +57,9 @@ void NGTextPainter::PaintInternalFragment(
     DCHECK(step == kPaintText);
     graphics_context_.DrawText(font_, fragment_paint_info,
                                FloatPoint(text_origin_));
+    // TODO(npm): Check that there are non-whitespace characters. See
+    // crbug.com/788444.
+    graphics_context_.GetPaintController().SetTextPainted();
   }
 }
 

third_party/WebKit/Source/platform/fonts/Font.cpp

@@ -129,7 +129,7 @@ void DrawBlobs(PaintCanvas* canvas,
 
 }  // anonymous ns
 
-bool Font::DrawText(PaintCanvas* canvas,
+void Font::DrawText(PaintCanvas* canvas,
                     const TextRunPaintInfo& run_info,
                     const FloatPoint& point,
                     float device_scale_factor,
@@ -137,7 +137,7 @@ bool Font::DrawText(PaintCanvas* canvas,
   // Don't draw anything while we are using custom fonts that are in the process
   // of loading.
   if (ShouldSkipDrawing())
-    return false;
+    return;
 
   ShapeResultBloberizer bloberizer(*this, device_scale_factor);
   CachingWordShaper word_shaper(*this);
@@ -145,10 +145,9 @@ bool Font::DrawText(PaintCanvas* canvas,
   word_shaper.FillResultBuffer(run_info, &buffer);
   bloberizer.FillGlyphs(run_info, buffer);
   DrawBlobs(canvas, flags, bloberizer.Blobs(), point);
-  return true;
 }
 
-bool Font::DrawText(PaintCanvas* canvas,
+void Font::DrawText(PaintCanvas* canvas,
                     const NGTextFragmentPaintInfo& text_info,
                     const FloatPoint& point,
                     float device_scale_factor,
@@ -156,13 +155,12 @@ bool Font::DrawText(PaintCanvas* canvas,
   // Don't draw anything while we are using custom fonts that are in the process
   // of loading.
   if (ShouldSkipDrawing())
-    return false;
+    return;
 
   ShapeResultBloberizer bloberizer(*this, device_scale_factor);
   bloberizer.FillGlyphs(text_info.text, text_info.from, text_info.to,
                         text_info.shape_result);
   DrawBlobs(canvas, flags, bloberizer.Blobs(), point);
-  return true;
 }
 
 bool Font::DrawBidiText(PaintCanvas* canvas,

third_party/WebKit/Source/platform/fonts/Font.h

@@ -81,12 +81,12 @@ class PLATFORM_EXPORT Font {
     kDoNotPaintIfFontNotReady,
     kUseFallbackIfFontNotReady
   };
-  bool DrawText(PaintCanvas*,
+  void DrawText(PaintCanvas*,
                 const TextRunPaintInfo&,
                 const FloatPoint&,
                 float device_scale_factor,
                 const PaintFlags&) const;
-  bool DrawText(PaintCanvas*,
+  void DrawText(PaintCanvas*,
                 const NGTextFragmentPaintInfo&,
                 const FloatPoint&,
                 float device_scale_factor,

third_party/WebKit/Source/platform/graphics/GraphicsContext.cpp

@@ -743,10 +743,8 @@ void GraphicsContext::DrawTextInternal(const Font& font,
   if (ContextDisabled())
     return;
 
-  if (font.DrawText(canvas_, text_info, point, device_scale_factor_,
-                    ApplyHighContrastFilter(&flags))) {
-    paint_controller_.SetTextPainted();
-  }
+  font.DrawText(canvas_, text_info, point, device_scale_factor_,
+                ApplyHighContrastFilter(&flags));
 }
 
 void GraphicsContext::DrawText(const Font& font,
@@ -790,9 +788,8 @@ void GraphicsContext::DrawTextInternal(const Font& font,
     return;
 
   DrawTextPasses([&font, &text_info, &point, this](const PaintFlags& flags) {
-    if (font.DrawText(canvas_, text_info, point, device_scale_factor_,
-                      ApplyHighContrastFilter(&flags)))
-      paint_controller_.SetTextPainted();
+    font.DrawText(canvas_, text_info, point, device_scale_factor_,
+                  ApplyHighContrastFilter(&flags));
   });
 }