Fix textLength position adjustment for the "adjust spacing" case

third_party/WebKit/LayoutTests/platform/mac/svg/text/select-textLength-spacing-stretch-2-expected.txt

+layer at (0,0) size 800x600
+  LayoutView at (0,0) size 800x600
+layer at (0,0) size 800x600
+  LayoutSVGRoot {svg} at (0,0) size 800x600
+    LayoutSVGContainer {g} at (61.86,1) size 14.49x11.20
+      LayoutSVGPath {svg:line} at (61.86,1) size 0x11.20 [stroke={[type=SOLID] [color=#008000]}] [fill={[type=SOLID] [color=#000000]}] [x1=61.86] [y1=1.00] [x2=61.86] [y2=12.20]
+      LayoutSVGPath {svg:line} at (76.35,1) size 0x11.20 [stroke={[type=SOLID] [color=#008000]}] [fill={[type=SOLID] [color=#000000]}] [x1=76.35] [y1=1.00] [x2=76.35] [y2=12.20]
+      LayoutSVGRect {svg:rect} at (61.86,1) size 14.49x11.20 [fill={[type=SOLID] [color=#FF0000] [opacity=0.40]}] [x=61.86] [y=1.00] [width=14.49] [height=11.20]
+    LayoutSVGText {text} at (10,1) size 149.98x11.19 contains 1 chunk(s)
+      LayoutSVGInlineText {#text} at (10,1) size 149.98x11.19
+        chunk 1 text run 1 at (10.00,10.00) startOffset 0 endOffset 1 width 6.11: "T"
+        chunk 1 text run 2 at (21.15,10.00) startOffset 1 endOffset 2 width 5.56: "e"
+        chunk 1 text run 3 at (32.86,10.00) startOffset 2 endOffset 3 width 5.00: "x"
+        chunk 1 text run 4 at (44.01,10.00) startOffset 3 endOffset 4 width 2.78: "t"
+        chunk 1 text run 5 at (52.94,10.00) startOffset 4 endOffset 5 width 2.78: " "
+        chunk 1 text run 6 at (61.86,10.00) startOffset 5 endOffset 6 width 2.78: "t"
+        chunk 1 text run 7 at (70.79,10.00) startOffset 6 endOffset 7 width 5.56: "o"
+        chunk 1 text run 8 at (82.50,10.00) startOffset 7 endOffset 8 width 2.78: " "
+        chunk 1 text run 9 at (91.43,10.00) startOffset 8 endOffset 9 width 6.67: "S"
+        chunk 1 text run 10 at (104.25,10.00) startOffset 9 endOffset 10 width 2.78: "t"
+        chunk 1 text run 11 at (113.17,10.00) startOffset 10 endOffset 11 width 3.33: "r"
+        chunk 1 text run 12 at (122.65,10.00) startOffset 11 endOffset 12 width 5.56: "e"
+        chunk 1 text run 13 at (134.36,10.00) startOffset 12 endOffset 13 width 2.78: "t"
+        chunk 1 text run 14 at (143.29,10.00) startOffset 13 endOffset 14 width 5.00: "c"
+        chunk 1 text run 15 at (154.44,10.00) startOffset 14 endOffset 15 width 5.56: "h"
+selection start: position 5 of child 0 {#text} of child 5 {text} of child 0 {svg} of document
+selection end:   position 7 of child 0 {#text} of child 5 {text} of child 0 {svg} of document