RFR: 8278268 - (ch) InputStream returned by Channels.newInputStream should have fast path for FileChannel targets [v7]

[Markus KARG]

> This sub-issue defines the work to be done to implement JDK-8265891 solely for the particular case of FileChannel.transferFrom(ReadableByteChannel), including special treatment of SelectableByteChannel.

Markus KARG has updated the pull request incrementally with two additional commits since the last revision:

 - Simplified using checked function
   
   Signed-off-by: Markus Karg <markus at headcrashing.eu>
 - Common implementation for all 2 GB tests
   
   Signed-off-by: Markus Karg <markus at headcrashing.eu>

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6711/files
  - new: https://git.openjdk.java.net/jdk/pull/6711/files/2579cef9..003c64c2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6711&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6711&range=05-06

  Stats: 81 lines in 1 file changed: 13 ins; 56 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6711.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6711/head:pull/6711

PR: https://git.openjdk.java.net/jdk/pull/6711