don't add baseUrl on clipPath URls when staticPlot:true

... but I'm not sure that's correct. We might still need that
    baseUrl for staticPlot:true graph don't get exported
    via Plotly.toImage or Plotly.downloadImage.

Author: etpinard

src/components/drawing/index.js

@@ -1005,7 +1005,7 @@ function nodeHash(node) {
  * note! We'd better not be exporting from a page
  * with a <base> or the svg will not be portable!
  */
-drawing.setClipUrl = function(s, localId) {
+drawing.setClipUrl = function(s, localId, gd) {
     if(!localId) {
         s.attr('clip-path', null);
         return;
@@ -1025,7 +1025,9 @@ drawing.setClipUrl = function(s, localId) {
         }
     }
 
-    s.attr('clip-path', 'url(' + drawing.baseUrl + '#' + localId + ')');
+    var baseUrl = gd._context.staticPlot ? '' : drawing.baseUrl;
+
+    s.attr('clip-path', 'url(' + baseUrl + '#' + localId + ')');
 };
 
 drawing.getTranslate = function(element) {

test/jasmine/tests/snapshot_test.js

@@ -1,5 +1,6 @@
 var Plotly = require('@lib/index');
 var Lib = require('@src/lib');
+var Drawing = require('@src/components/drawing');
 
 var d3 = require('d3');
 var createGraphDiv = require('../assets/create_graph_div');
@@ -367,5 +368,37 @@ describe('Plotly.Snapshot', function() {
             .catch(failTest)
             .then(done);
         });
+
+        it('should work on pages with <base>', function(done) {
+            delete Drawing.baseUrl;
+            var base = d3.select('body')
+                .append('base')
+                .attr('href', 'https://plot.ly');
+
+            Plotly.plot(gd, [{ y: [1, 2, 1] }], {}, {staticPlot: true})
+            .then(function() { return Plotly.Snapshot.toSVG(gd); })
+            .then(function(svg) {
+                var svgDOM = parser.parseFromString(svg, 'image/svg+xml');
+                var gSubplot = svgDOM.getElementsByClassName('plot')[0];
+                var clipPath = gSubplot.getAttribute('clip-path');
+                var len = clipPath.length;
+
+                var head = clipPath.substr(0, 4);
+                var tail = clipPath.substr(len - 7, len);
+                expect(head).toBe('url(', 'subplot clipPath head');
+                expect(tail).toBe('xyplot)', 'subplot clipPath tail');
+
+                var middle = clipPath.substr(5, 10);
+                expect(middle.length).toBe(10, 'subplot clipPath uid length');
+                expect(middle.indexOf('http://')).toBe(-1, 'no <base> URL in subplot clipPath!');
+                expect(middle.indexOf('https://')).toBe(-1, 'no <base> URL in subplot clipPath!');
+            })
+            .catch(failTest)
+            .then(function() {
+                base.remove();
+                delete Drawing.baseUrl;
+                done();
+            });
+        });
     });
 });