Stricter treatment of SVGSVGElement::m_useCurrentView

m_useCurrentView being true implies that m_viewSpec is non-null. Perhaps
defensively, most code that checks it is written in a way such that it
expects that m_viewSpec can be null if m_useCurrentView is true - which
is not the case, and adds unnecessary code.
Instead change the code to adhere to the rule above, and assert that in
the various places instead.
Also add some checks of the invariant in methods that set the flag and
m_viewSpec. Refactor SVGSVGElement::setupInitialView to avoid the need
to sprinkle invariant checks "all over" it.

BUG=110195

Review-Url: https://codereview.chromium.org/2290293003
Cr-Commit-Position: refs/heads/master@{#415346}

third_party/WebKit/Source/core/svg/SVGSVGElement.cpp

@@ -99,7 +99,7 @@ SVGViewSpec* SVGSVGElement::currentView()
 {
     if (!m_viewSpec)
         m_viewSpec = SVGViewSpec::create(this);
-    return m_viewSpec.get();
+    return m_viewSpec;
 }
 
 float SVGSVGElement::currentScale() const
@@ -161,8 +161,9 @@ bool SVGSVGElement::zoomAndPanEnabled() const
 {
     const SVGZoomAndPan* currentViewSpec = this;
     if (m_useCurrentView)
-        currentViewSpec = m_viewSpec.get();
-    return currentViewSpec && currentViewSpec->zoomAndPan() == SVGZoomAndPanMagnify;
+        currentViewSpec = m_viewSpec;
+    DCHECK(currentViewSpec);
+    return currentViewSpec->zoomAndPan() == SVGZoomAndPanMagnify;
 }
 
 void SVGSVGElement::parseAttribute(const QualifiedName& name, const AtomicString& oldValue, const AtomicString& value)
@@ -568,8 +569,10 @@ bool SVGSVGElement::selfHasRelativeLengths() const
 
 FloatRect SVGSVGElement::currentViewBoxRect() const
 {
-    if (m_useCurrentView)
-        return m_viewSpec ? m_viewSpec->viewBox()->currentValue()->value() : FloatRect();
+    if (m_useCurrentView) {
+        DCHECK(m_viewSpec);
+        return m_viewSpec->viewBox()->currentValue()->value();
+    }
 
     FloatRect useViewBox = viewBox()->currentValue()->value();
     if (!useViewBox.isEmpty())
@@ -628,8 +631,9 @@ float SVGSVGElement::intrinsicHeight() const
 
 AffineTransform SVGSVGElement::viewBoxToViewTransform(float viewWidth, float viewHeight) const
 {
-    if (!m_useCurrentView || !m_viewSpec)
+    if (!m_useCurrentView)
         return SVGFitToViewBox::viewBoxToViewTransform(currentViewBoxRect(), preserveAspectRatio()->currentValue(), viewWidth, viewHeight);
+    DCHECK(m_viewSpec);
 
     AffineTransform ctm = SVGFitToViewBox::viewBoxToViewTransform(currentViewBoxRect(), m_viewSpec->preserveAspectRatio()->currentValue(), viewWidth, viewHeight);
     SVGTransformList* transformList = m_viewSpec->transform();
@@ -645,41 +649,39 @@ AffineTransform SVGSVGElement::viewBoxToViewTransform(float viewWidth, float vie
 
 void SVGSVGElement::setupInitialView(const String& fragmentIdentifier, Element* anchorNode)
 {
-    LayoutObject* layoutObject = this->layoutObject();
-    SVGViewSpec* view = m_viewSpec.get();
-    if (view)
-        view->reset();
+    if (m_viewSpec)
+        m_viewSpec->reset();
 
-    bool hadUseCurrentView = m_useCurrentView;
+    // If we previously had a view, we need to layout again, regardless of the
+    // state after setting.
+    bool needsViewUpdate = m_useCurrentView;
     m_useCurrentView = false;
 
     if (fragmentIdentifier.startsWith("svgView(")) {
-        if (!view)
-            view = currentView(); // Create the SVGViewSpec.
+        SVGViewSpec* view = currentView(); // Ensure the SVGViewSpec has been created.
 
         view->inheritViewAttributesFromElement(this);
 
         if (view->parseViewSpec(fragmentIdentifier)) {
             UseCounter::count(document(), UseCounter::SVGSVGElementFragmentSVGView);
             m_useCurrentView = true;
+            needsViewUpdate = true;
         } else {
             view->reset();
         }
-
-        if (layoutObject && (hadUseCurrentView || m_useCurrentView))
-            markForLayoutAndParentResourceInvalidation(layoutObject);
-        return;
-    }
-
-    // Spec: If the SVG fragment identifier addresses a 'view' element within an SVG document (e.g., MyDrawing.svg#MyView
-    // or MyDrawing.svg#xpointer(id('MyView'))) then the closest ancestor 'svg' element is displayed in the viewport.
-    // Any view specification attributes included on the given 'view' element override the corresponding view specification
-    // attributes on the closest ancestor 'svg' element.
-    // TODO(ed): The spec text above is a bit unclear.
-    // Should the transform from outermost svg to nested svg be applied to "display"
-    // the inner svg in the viewport, then let the view element override the inner
-    // svg's view specification attributes. Should it fill/override the outer viewport?
-    if (isSVGViewElement(anchorNode)) {
+    } else if (isSVGViewElement(anchorNode)) {
+        // Spec: If the SVG fragment identifier addresses a 'view' element
+        // within an SVG document (e.g., MyDrawing.svg#MyView or
+        // MyDrawing.svg#xpointer(id('MyView'))) then the closest ancestor
+        // 'svg' element is displayed in the viewport.  Any view specification
+        // attributes included on the given 'view' element override the
+        // corresponding view specification attributes on the closest ancestor
+        // 'svg' element.
+        // TODO(ed): The spec text above is a bit unclear.
+        // Should the transform from outermost svg to nested svg be applied to
+        // "display" the inner svg in the viewport, then let the view element
+        // override the inner svg's view specification attributes. Should it
+        // fill/override the outer viewport?
         SVGViewElement& viewElement = toSVGViewElement(*anchorNode);
 
         if (SVGSVGElement* svg = viewElement.ownerSVGElement()) {
@@ -692,11 +694,13 @@ void SVGSVGElement::setupInitialView(const String& fragmentIdentifier, Element*
         }
     }
 
-    // If we previously had a view and didn't get a new one, we need to
-    // layout again.
-    if (layoutObject && hadUseCurrentView)
+    LayoutObject* layoutObject = this->layoutObject();
+    if (layoutObject && needsViewUpdate)
         markForLayoutAndParentResourceInvalidation(layoutObject);
 
+    // If m_useCurrentView is true we should have a view-spec.
+    DCHECK(!m_useCurrentView || m_viewSpec);
+
     // FIXME: We need to decide which <svg> to focus on, and zoom to it.
     // FIXME: We need to actually "highlight" the viewTarget(s).
 }
@@ -708,6 +712,7 @@ void SVGSVGElement::inheritViewAttributes(SVGViewElement* viewElement)
     UseCounter::count(document(), UseCounter::SVGSVGElementFragmentSVGViewElement);
     view->inheritViewAttributesFromElement(this);
     view->inheritViewAttributesFromElement(viewElement);
+    DCHECK(!m_useCurrentView || m_viewSpec);
 }
 
 void SVGSVGElement::finishParsingChildren()