In url
String url="http://chart.apis.google.com/chart?&cht=lc&chco=000000&chds=0,10&chdlp=b&chxt=x,y"
+"&chg=1.04,0,5,1&chds=0,30&chco=3072F3,ff0000,00aaaa&chls=2,4,1&chm=s,FF0000,0,-1,0|s,0000ff,1,-1,0|s,00aa00,2,-1,0"
+"&chs=480x280&chof=validate&chd=t:100,200,300,400,500,600,700&chd=t:"
+point;
Your point is converted with point.toString() and appended to the url in this part
"&chd=t:"+point;
which is the second time when chd appers in the url. So in effect only the last chd value is considered. And the first which was chd=t:100,200,300,400,500,600,700 is not considered.
If you want to pass chd it has to be in format chd=t:val,val,val where val represents a value from your data. See an example with a data chd=t:-5,30,-30,50,80,200
and chd should appear only once in the url.
So your code for the url would be this:
String url="http://chart.apis.google.com/chart?&cht=lc&chco=000000&chds=0,10&chdlp=b&chxt=x,y"
+ "&chg=1.04,0,5,1&chds=0,30&chco=3072F3,ff0000,00aaaa&chls=2,4,1&chm=s,FF0000,0,-1,0|s,0000ff,1,-1,0|s,00aa00,2,-1,0"
+ "&chs=480x280&chof=validate&chd=t:"+<comma separated list of values>;