stagefright: add AString constructor from String8

namespace android {

struct String8;

struct AString {

    AString();

    AString(const char *s);

    AString(const char *s, size_t size);

    AString(const String8 &from);

    AString(const AString &from);

    AString(const AString &from, size_t offset, size_t n);

    ~AString();

#include <stdlib.h>

#include <string.h>

#include <utils/String8.h>

#include "ADebug.h"

#include "AString.h"

    setTo(s, size);

}

AString::AString(const String8 &from)

    : mData(NULL),

      mSize(0),

      mAllocSize(1) {

    setTo(from.string(), from.length());

}

AString::AString(const AString &from)

    : mData(NULL),

      mSize(0),