Fix first-line text-transform workaround when start is not zero

r526281 added a workaround for when text-transform shorten
the string, but did so only for when inline_text_box_.Start()
is zero.

This patch extends the workaround for when inline_text_box_.
Start() is not zero.

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ib4536ae5aaf92352e41ef19e53c2046a4c86806c
Bug: 880176, 795498
Reviewed-on: https://chromium-review.googlesource.com/1218202
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590194}

third_party/WebKit/LayoutTests/fast/text/firstline/capitalize-transform.html

@@ -6,7 +6,7 @@
 <script src="../../../resources/testharnessreport.js"></script>
 <!-- The capitalized form of the text below has only one character, whereas
 the lowercase has two. -->
-<div lang=el>ά</div>
+<div lang=el> ά</div>
 <div id=target></div>
 <script>
 test(function() {

third_party/blink/renderer/core/paint/inline_text_box_painter.cc

@@ -194,13 +194,15 @@ void InlineTextBoxPainter::Paint(const PaintInfo& paint_info,
     // capitalizing letters can change the length of the backing string.
     // That needs to be taken into account when computing the size of the box
     // or its painting.
-    length = std::min(length, first_line_string.length());
+    length = std::min(length, first_line_string.length() -
+                                  std::min(inline_text_box_.Start(),
+                                           first_line_string.length()));
 
     // TODO(szager): Figure out why this CHECK sometimes fails, it shouldn't.
-    CHECK(inline_text_box_.Start() + length <= first_line_string.length());
+    CHECK_LE(inline_text_box_.Start() + length, first_line_string.length());
   } else {
     // TODO(szager): Figure out why this CHECK sometimes fails, it shouldn't.
-    CHECK(inline_text_box_.Start() + length <= layout_item_string.length());
+    CHECK_LE(inline_text_box_.Start() + length, layout_item_string.length());
   }
   StringView string =
       StringView(inline_text_box_.IsFirstLineStyle() ? first_line_string