Add Blink-side flag for enabling/disabling layer squashing.

Source/core/testing/InternalSettings.cpp

Index: Source/core/testing/InternalSettings.cpp
diff --git a/Source/core/testing/InternalSettings.cpp b/Source/core/testing/InternalSettings.cpp
index 467504fe7800e136f57a04a3a631d0b642221dec..04abe815a93e5965583a317dd78291f8bdfecc6b 100644
--- a/Source/core/testing/InternalSettings.cpp
+++ b/Source/core/testing/InternalSettings.cpp
@@ -75,6 +75,7 @@ InternalSettings::Backup::Backup(Settings* settings)
     , m_shouldDisplayTextDescriptions(settings->shouldDisplayTextDescriptions())
     , m_defaultVideoPosterURL(settings->defaultVideoPosterURL())
     , m_originalCompositorDrivenAcceleratedScrollEnabled(settings->isCompositorDrivenAcceleratedScrollingEnabled())
+    , m_originalLayerSquashingEnabled(settings->isLayerSquashingEnabled())
     , m_originalPasswordGenerationDecorationEnabled(settings->passwordGenerationDecorationEnabled())
 {
 }
@@ -99,6 +100,7 @@ void InternalSettings::Backup::restoreTo(Settings* settings)
     settings->setShouldDisplayTextDescriptions(m_shouldDisplayTextDescriptions);
     settings->setDefaultVideoPosterURL(m_defaultVideoPosterURL);
     settings->setCompositorDrivenAcceleratedScrollingEnabled(m_originalCompositorDrivenAcceleratedScrollEnabled);
+    settings->setLayerSquashingEnabled(m_originalLayerSquashingEnabled);
     settings->setPasswordGenerationDecorationEnabled(m_originalPasswordGenerationDecorationEnabled);
     settings->resetFontFamilies();
 }
@@ -206,6 +208,14 @@ void InternalSettings::setCompositorDrivenAcceleratedScrollingEnabled(bool enabl
     settings()->setCompositorDrivenAcceleratedScrollingEnabled(enabled);
 }
 
+// FIXME: This is a temporary flag and should be removed once squashing is
+// ready (crbug.com/261605).
+void InternalSettings::setLayerSquashingEnabled(bool enabled, ExceptionState& exceptionState)
+{
+    InternalSettingsGuardForSettings();
+    settings()->setLayerSquashingEnabled(enabled);
+}
+
 typedef void (Settings::*SetFontFamilyFunction)(const AtomicString&, UScriptCode);
 static void setFontFamily(Settings* settings, const String& family, const String& script, SetFontFamilyFunction setter)
 {