Update RenderText::text() to return a String instead of a StringImpl

https://bugs.webkit.org/show_bug.cgi?id=268918

Reviewed by Alan Baradlay.

Update RenderText::text() to return a String instead of a StringImpl. It is safe
 to deal with Strings than with StringImpl pointers directly. There is also zero
 performance difference on Speedometer 2 & 3.

* Source/WebCore/editing/TextIterator.cpp:
(WebCore::collapsedSpaceLength):
* Source/WebCore/layout/integration/LayoutIntegrationBoxTree.cpp:
(WebCore::LayoutIntegration::BoxTree::createLayoutBox):
(WebCore::LayoutIntegration::BoxTree::updateContent):
* Source/WebCore/rendering/RenderText.h:
(WebCore::RenderText::text const):

Canonical link: https://commits.webkit.org/274220@main

Source/WebCore/editing/TextIterator.cpp

@@ -939,7 +939,7 @@ static bool shouldEmitExtraNewlineForNode(Node& node)
 
 static int collapsedSpaceLength(RenderText& renderer, int textEnd)
 {
-    StringImpl& text = renderer.text();
+    auto text = renderer.text();
     unsigned length = text.length();
     for (unsigned i = textEnd; i < length; ++i) {
         if (!renderer.style().isCollapsibleWhiteSpace(text[i]))

Source/WebCore/layout/integration/LayoutIntegrationBoxTree.cpp

@@ -193,7 +193,7 @@ UniqueRef<Layout::Box> BoxTree::createLayoutBox(RenderObject& renderer)
         auto isCombinedText = is<RenderCombineText>(textRenderer) && downcast<RenderCombineText>(textRenderer).isCombined();
         auto text = style.textSecurity() == TextSecurity::None
             ? (isCombinedText ? textRenderer.originalText() : textRenderer.text())
-            : RenderBlock::updateSecurityDiscCharacters(style, isCombinedText ? textRenderer.originalText() : textRenderer.text());
+            : RenderBlock::updateSecurityDiscCharacters(style, isCombinedText ? textRenderer.originalText() : String { textRenderer.text() });
 
         auto canUseSimpleFontCodePath = textRenderer.canUseSimpleFontCodePath();
         auto canUseSimplifiedTextMeasuring = textRenderer.canUseSimplifiedTextMeasuring();
@@ -295,7 +295,7 @@ void BoxTree::updateContent(const RenderText& textRenderer)
     auto& inlineTextBox = downcast<Layout::InlineTextBox>(layoutBoxForRenderer(textRenderer));
     auto& style = inlineTextBox.style();
     auto isCombinedText = is<RenderCombineText>(textRenderer) && downcast<RenderCombineText>(textRenderer).isCombined();
-    auto text = style.textSecurity() == TextSecurity::None ? (isCombinedText ? textRenderer.originalText() : textRenderer.text()) : RenderBlock::updateSecurityDiscCharacters(style, isCombinedText ? textRenderer.originalText() : textRenderer.text());
+    auto text = style.textSecurity() == TextSecurity::None ? (isCombinedText ? textRenderer.originalText() : String { textRenderer.text() }) : RenderBlock::updateSecurityDiscCharacters(style, isCombinedText ? textRenderer.originalText() : String { textRenderer.text() });
     auto contentCharacteristic = OptionSet<Layout::InlineTextBox::ContentCharacteristic> { };
     if (textRenderer.canUseSimpleFontCodePath())
         contentCharacteristic.add(Layout::InlineTextBox::ContentCharacteristic::CanUseSimpledFontCodepath);

Source/WebCore/rendering/RenderText.h

@@ -68,7 +68,7 @@ class RenderText : public RenderObject {
     void attachTextBox(LegacyInlineTextBox& box) { m_lineBoxes.attach(box); }
     void removeTextBox(LegacyInlineTextBox& box) { m_lineBoxes.remove(box); }
 
-    StringImpl& text() const { return *m_text.impl(); } // Since m_text can never be null, returning this type means callers won't null check.
+    const String& text() const { return m_text; }
     String textWithoutConvertingBackslashToYenSymbol() const;
 
     LegacyInlineTextBox* createInlineTextBox() { return m_lineBoxes.createAndAppendLineBox(*this); }