Add srcset negative x descriptor value tests

The implementation handled negative x descriptors properly, but they weren't tested.

This CL fixes that.

BUG=376726
CC=simonp@opera.com

Review URL: https://codereview.chromium.org/292383004

git-svn-id: svn://svn.chromium.org/blink/trunk@175033 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/html/parser/HTMLSrcsetParserTest.cpp

@@ -25,6 +25,9 @@ TEST(HTMLSrcsetParserTest, Basic)
     TestCase testCases[] = {
         {2.0, -1, "", "1x.gif 1x, 2x.gif 2x", "2x.gif", 2.0, -1},
         {2.0, -1, "", "1x.gif 1x, 2x.gif -2x", "1x.gif", 1.0, -1},
+        {2.0, -1, "", "0x.gif 0x", "0x.gif", 0.0, -1},
+        {2.0, -1, "", "0x.gif -0x", "0x.gif", 0.0, -1},
+        {2.0, -1, "", "neg.gif -2x", "", 1.0, -1},
         {2.0, -1, "", "1x.gif 1x, 2x.gif 2q", "1x.gif", 1.0, -1},
         {2.0, -1, "1x.gif 1x, 2x.gif 2x", "1x.gif 1x, 2x.gif 2x", "2x.gif", 2.0, -1},
         {1.0, -1, "1x.gif 1x, 2x.gif 2x", "1x.gif 1x, 2x.gif 2x", "1x.gif", 1.0, -1},