Don't tear down renderer and other busy work when Svg::setImagePath is invoked with the same arg

Summary:
During my plasmashell startup this saves time for 17 calls. Opening
something like Simple Menu saves another ~dozen.

It's worth investigating why Svg::setImagePath gets called repeatedly
with the same args to begin with, but this is worth doing anyway.

Reviewers: #plasma, davidedmundson, mart

Subscribers: plasma-devel, #frameworks

Tags: #plasma, #frameworks

Differential Revision: https://phabricator.kde.org/D9115

src/plasma/private/svg_p.h

@@ -103,6 +103,7 @@ public:
     QHash<QString, QRectF> localRectCache;
     QHash<QString, QSize> elementsWithSizeHints;
     SharedSvgRenderer::Ptr renderer;
+    QString requestedPath;
     QString themePath;
     QString path;
     QSizeF size;

src/plasma/svg.cpp

@@ -182,6 +182,12 @@ QString SvgPrivate::cachePath(const QString &path, const QSize &size) const
 
 bool SvgPrivate::setImagePath(const QString &imagePath)
 {
+    if (requestedPath == imagePath) {
+        return false;
+    }
+
+    requestedPath = imagePath;
+
     QString actualPath = imagePath;
     if (imagePath.startsWith(QLatin1String("file://"))) {
         //length of file://