Tracing for developers of native methods.

The existing -verbose:jni is mainly useful for VM developers hacking on the JNI
implementation; this is intended to replace the ad hoc logging developers of
native methods need to write.

Use "-Xint:portable -Xjnitrace:ClassNameSubstring" on the command line. To
trace all native methods (mainly useful for testing the tracing), use
"-Xjnitrace:"; to trace just methods in java.util.regex.Matcher, use
"-Xjnitrace:Matcher" or "-Xjnitrace:Ljava/util/regex/Matcher;" or whatever.
To trace all the methods in Matcher and Pattern, you have to use something
like "-Xjnitrace:java/util/regex/". There's no facility for tracing an
individual method or group of methods because I haven't needed such a thing.

Here's a basic example:

 -> Ljava/nio/charset/Charsets;.toUtf8Bytes([CII)[B (0x400474b8, 0, 5)
 <- Ljava/nio/charset/Charsets;.toUtf8Bytes([CII)[B returned 0x40047548

Here's an example of a non-static native method:

 -> Lorg/apache/harmony/luni/platform/OSFileSystem;.writeImpl(I[BII)J this=0x40012e78 (1, 0x400476d0, 0, 5)
 <- Lorg/apache/harmony/luni/platform/OSFileSystem;.writeImpl(I[BII)J returned 5

Here's an interesting example showing another native method being called, and
an exception being thrown by a native method:

 -> Ljava/lang/VMClassLoader;.loadClass(Ljava/lang/String;Z)Ljava/lang/Class; (0x400466b8, false)
 -> Ljava/lang/Throwable;.nativeFillInStackTrace()Ljava/lang/Object; ()
 <- Ljava/lang/Throwable;.nativeFillInStackTrace()Ljava/lang/Object; returned 0x400467c8
 <- Ljava/lang/VMClassLoader;.loadClass(Ljava/lang/String;Z)Ljava/lang/Class; threw Ljava/lang/ClassNotFoundException;

(This functionality needs to be enabled at compile time. A later patch will
address that.)

Change-Id: I6da8930bd4b4f228e07b05cc59a3aea331c5cee1

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