RFR: 8215380: Backout accidental change to String::length

[Claes Redestad]

Hi,

I need to revert an accidental change to String.length

Bug: https://bugs.openjdk.java.net/browse/JDK-8215380
Patch inlined below

Running the accidentally pushed version in naive microbenchmarks showed
that avoiding the shift operation can improve throughput of str.length()
by a small measure (~1.06x) for latin1-only inputs, neutral for mixed
or utf16-only inputs, but also adds a branch (visible in profiling)
which could blow up in more real cases. Regardless, it should be
reviewed and discussed on it's own merits. Sorry!

/Claes

diff -r 8bf9268df0e2 src/java.base/share/classes/java/lang/String.java
--- a/src/java.base/share/classes/java/lang/String.java	Thu Dec 13 
15:31:05 2018 +0100
+++ b/src/java.base/share/classes/java/lang/String.java	Thu Dec 13 
23:59:43 2018 +0100
@@ -664,7 +664,7 @@
       *          object.
       */
      public int length() {
-        return isLatin1() ? value.length : value.length >> UTF16;
+        return value.length >> coder();
      }

      /**