Disable page shrinking for pdf printing to create accurate output

PDFs are not rendered like PNG or other image formats by phantomjs because it
uses the printer functionality of Qt+Webkit. But Webkit uses some printer
"optimization" to save paper by shrinking the output. Such shrinking results in
too small content on a page.

https://github.com/ariya/phantomjs/issues/11590 ("page.paperSize is not
accurate for .pdf")

src/qt/src/3rdparty/webkit/Source/WebCore/page/PrintContext.cpp

@@ -35,13 +35,13 @@ namespace WebCore {
 // print in IE and Camino. This lets them use fewer sheets than they
 // would otherwise, which is presumably why other browsers do this.
 // Wide pages will be scaled down more than this.
-const float printingMinimumShrinkFactor = 1.25f;
+const float printingMinimumShrinkFactor = 1;
 
 // This number determines how small we are willing to reduce the page content
 // in order to accommodate the widest line. If the page would have to be
 // reduced smaller to make the widest line fit, we just clip instead (this
 // behavior matches MacIE and Mozilla, at least)
-const float printingMaximumShrinkFactor = 2;
+const float printingMaximumShrinkFactor = 1;
 
 PrintContext::PrintContext(Frame* frame)
     : m_frame(frame)