Summary
-------

Add the options "file=<file>" to JMap -histo to improve JMap's ability

Problem
-------

Currently the "JMap -histo" tool doesn't support to dump result to a file directly.

Solution
--------

Add "file=<file>" option that let JMap -histo to dump directly to file. 
Please be aware that this is subset of  enhancement of JMap More detail please refer to https://bugs.openjdk.java.net/browse/JDK-8214535

Specification
-------------

Diff:

    --- old/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java
    +++ new/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java
    @@ -246,21 +266,27 @@
             System.err.println("        to connect to running process and print class loader statistics");
             System.err.println("    jmap -finalizerinfo <pid>");
             System.err.println("        to connect to running process and print information on objects awaiting finalization");
    -        System.err.println("    jmap -histo[:live] <pid>");
    +        System.err.println("    jmap -histo[:[<histo-options>]] <pid>");
             System.err.println("        to connect to running process and print histogram of java object heap");
    -        System.err.println("        if the \"live\" suboption is specified, only count live objects");
             System.err.println("    jmap -dump:<dump-options> <pid>");
             System.err.println("        to connect to running process and dump java heap");
             System.err.println("    jmap -? -h --help");
             System.err.println("        to print this help message");
             System.err.println("");
             System.err.println("    dump-options:");
    -        System.err.println("      live         dump only live objects; if not specified,");
    -        System.err.println("                   all objects in the heap are dumped.");
    +        System.err.println("      live         dump only live objects");
    +        System.err.println("      all          dump all objects in the heap (default if one of \"live\" or \"all\" is not specified);
             System.err.println("      format=b     binary format");
             System.err.println("      file=<file>  dump heap to <file>");
             System.err.println("");
             System.err.println("    Example: jmap -dump:live,format=b,file=heap.bin <pid>");
    +        System.err.println("");
    +        System.err.println("    histo-options:");
    +        System.err.println("      live         count only live objects");
    +        System.err.println("      all          count all objects in the heap (default if one of \"live\" or \"all\" is not specified)");
    +        System.err.println("      file=<file>  dump data to <file>");
    +        System.err.println("");
    +        System.err.println("    Example: jmap -histo:live,file=/tmp/histo.data <pid>");
             System.exit(exit);
        }   
    }

Updated specification:

    jmap -clstats <pid>
        to connect to running process and print class loader statistics
    jmap -finalizerinfo <pid>
        to connect to running process and print information on objects awaiting finalization
    jmap -histo[:<histo-options>] <pid>
        to connect to running process and print histogram of java object heap
    jmap -dump:<dump-options> <pid>
        to connect to running process and dump java heap
    jmap -? -h --help
        to print this help message

    dump-options:
      live         dump only live objects; if not specified, use "all".
      all          all objects in the heap are dumped.
      format=b     binary format
      file=<file>  dump heap to <file>

    Example: jmap -dump:live,format=b,file=heap.bin <pid>

    histo-options:
      live         only count live objects; if not specified, use "all".
      all          count all objects in the heap
      file=<file>  dump data to <file>

    Example: jmap -histo:live,file=/tmp/histo.data <pid>