Simplify svg/custom/invisible-text-after-scrolling.xhtml

This test generates a lot of <text> elements that will never be made
visible by the test as currently written. Reduce the number of <text>
elements to only those that will potentially intersect the viewport of
the scrollable container during the test.

Bug: 571296
Change-Id: I048516e4084cb4101a4058ee89b973d2cca7f338
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2215849
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Auto-Submit: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771798}

third_party/blink/web_tests/svg/custom/invisible-text-after-scrolling.xhtml

@@ -7,14 +7,14 @@
     <![CDATA[
         function runText() 
         {
-            for(var y=20; y<5000; y+=100)
+            for(var y=0; y<=1000; y+=100)
             {
-                for(var x=0; x<5000; x+=100)
+                for(var x=0; x<=500; x+=100)
                 {
                     var svgArea = document.getElementById("svgArea");
                     var text = document.createElementNS("http://www.w3.org/2000/svg", "text");
                     text.setAttributeNS(null, "x", x);
-                    text.setAttributeNS(null, "y", y);
+                    text.setAttributeNS(null, "y", y+20);
                     text.setAttributeNS(null, "fill", "black");
                     text.setAttributeNS(null, "font-size", 20);
                     text.setAttributeNS(null, "text-anchor", "start");