Serialize <number> to round to at most 6 decimals

LayoutTests/fast/css/round-trip-values-expected.txt

 For each input on the left, this table lists what happens when you pass it into a CSS property and retrieve its value back. The third column indicates whether the value was round-tripped faithfully.
 
 Basic floats
 '0.0001'        0.0001  pass
 0.0001  0.0001  pass
-'123456.123456' 123456.123456   pass
-'1234567.1234567'       1234567.1234567 pass
-'12345678.12345678'     12345678.1234568        pass
+'123456.123456' 123456  pass
+'1234567.1234567'       1.23457e+06     pass
+'12345678.12345678'     1.23457e+07     pass
 Trailing zeros
 '0.00100000'    0.001   pass
-'0.001000001'   0.001000001     pass
-'0.12345000001' 0.12345000001   pass
-'0.12304567'    0.12304567      pass
-'0.12340567'    0.12340567      pass
-'0.12345067'    0.12345067      pass
-'0.12345607'    0.12345607      pass
-'0.12345670'    0.1234567       pass
+'0.001000001'   0.001   pass
+'0.12345000001' 0.12345 pass
+'0.12304567'    0.123046        pass
+'0.12340567'    0.123406        pass
+'0.12345067'    0.123451        pass
+'0.12345607'    0.123456        pass
+'0.12345670'    0.123457        pass
 Repeating decimals
-1/3     0.333333333333333       pass
-123 + 1/3       123.333333333333        pass
-13/99   0.131313131313131       pass
-123 + 13/99     123.131313131313        pass
-100/999 0.1001001001001 pass
-123 + 100/999   123.1001001001  pass
+1/3     0.333333        pass
+123 + 1/3       123.333 pass
+13/99   0.131313        pass
+123 + 13/99     123.131 pass
+100/999 0.1001  pass
+123 + 100/999   123.1   pass
 Large numbers
-12345678        12345678        pass
-123456789       123456789       pass
-1234567890      1234567890      pass
-12345678901     12345678901     pass
-123456789012    123456789012    pass
-1234567890123   1234567890123   pass
-12345678901234  12345678901234  pass
-123456789012345 123456789012345 pass
-1234567890123456        1234567890123456        pass
-12345678901234567       12345678901234568       pass
+12345678        1.23457e+07     pass
+123456789       1.23457e+08     pass
+1234567890      1.23457e+09     pass
+12345678901     1.23457e+10     pass
+123456789012    1.23457e+11     pass
+1234567890123   1.23457e+12     pass
+12345678901234  1.23457e+13     pass
+123456789012345 1.23457e+14     pass
+1234567890123456        1.23457e+15     pass
+12345678901234567       1.23457e+16     pass
 Weird numbers
-Number.NaN      12345678901234568       pass
-1/0     12345678901234568       pass
-Math.sqrt(-1)   12345678901234568       pass
-1/0.9999        1.000100010001  pass
-1/0.99999       1.0000100001    pass
-1/0.999999      1.000001000001  pass
-1/0.9999999     1.00000010000001        pass
-1/0.99999999    1.00000001      pass
+Number.NaN      1.23457e+16     pass
+1/0     1.23457e+16     pass
+Math.sqrt(-1)   1.23457e+16     pass
+1/0.9999        1.0001  pass
+1/0.99999       1.00001 pass
+1/0.999999      1       pass
+1/0.9999999     1       pass
+1/0.99999999    1       pass