Fix percent height calc for svg docs.

third_party/WebKit/LayoutTests/svg/custom/masking-clipping-hidpi.svg

 <svg xmlns="http://www.w3.org/2000/svg" onload="startTest()">
     <script>
+    if (self.internals)

[pdr., 2017/04/26 04:56:47]

This test doesn't fail for me without the patch (OSX). Does it fail for you? I
tried with other flags such as --root-layer-scrolls but still couldn't get it to
fail.

I found a few tests that did run the code above (e.g., set relayout_children =
true;) such as svg/custom/svg-image-initial-size.html but these seem to pass
without the change. Why do these tests hit the new code but aren't affected by
it?

The testrunner has some special svg sizing code. Is it possible to reproduce
this outside the testrunner?

Can you add a simpler test? I had trouble digging much deeper in this review
without being able to repro.

[szager1, 2017/04/26 12:11:35]

It fails for me on linux.
 
As I mentioned in another comment, this doesn't typically manifest on first
layout, because the frame view size is stable by the time first layout runs. 
It's the call to setBackingScaleFactor after first layout that causes the
problem.
I couldn't figure out how to change the zoom factor from a unit test. 
ChromeClient doesn't offer anything useful.
I can add a simpler test, but if this one doesn't reproduce for you, then most
likely a simplified test won't reproduce either.

+        internals.runtimeFlags.overlayScrollbarsEnabled = true;
+        
     function startTest() {
         if (!window.testRunner)
             return;
 
         testRunner.waitUntilDone();
         testRunner.setBackingScaleFactor(2, finishTest);
     }
 
     function finishTest() {
         setTimeout(function () { testRunner.notifyDone(); }, 0);
@@ skipping 30 matching lines @@
     </defs>
     <rect x="0" y="60" width="100" height="100" clip-path="url(#circleClipPath)"/>
 
     <defs>
         <pattern id="Pattern" width="1" height="1">
             <circle cx="25" cy="25" r="20" fill="url(#blackGradient)"/>
         </pattern>
     </defs>
     <rect fill="url(#Pattern)" x="0" y="162" width="200" height="200"/>
 </svg>