Add SharedMemory.fromFileDescriptor

- Rename existing SharedMemory.create and make it public
- Passed file is now detached after creating shared memory and is
  not usable any more.

Bug: 188780895
CTS-Coverage-Bug: 197226773
Test: atest com.android.car.internal.test.LargeParcelableJavaStableAIDLTest
      (runs only in auto. will add matching CTS tests for non-auto devices)

(This combines two CL in internal tree, so Change-Id and Merged-In id are
different)
Change-Id: I8a634062d10ff0c114f3add1d2a5e8056f17b788
Merged-In: I11381e78580b97982b25a52aa06f2192def7353f

core/api/current.txt

@@ -30329,6 +30329,7 @@ package android.os {
     method public void close();
     method @NonNull public static android.os.SharedMemory create(@Nullable String, int) throws android.system.ErrnoException;
     method public int describeContents();
+    method @NonNull public static android.os.SharedMemory fromFileDescriptor(@NonNull android.os.ParcelFileDescriptor);
     method public int getSize();
     method @NonNull public java.nio.ByteBuffer map(int, int, int) throws android.system.ErrnoException;
     method @NonNull public java.nio.ByteBuffer mapReadOnly() throws android.system.ErrnoException;

core/java/android/os/SharedMemory.java

@@ -93,6 +93,26 @@ public final class SharedMemory implements Parcelable, Closeable {
         }
     }
 
+    /**
+     * Creates an instance from existing shared memory passed as {@link ParcelFileDescriptor}.
+     *
+     * <p> The {@code fd} should be a shared memory created from
+       {@code SharedMemory or ASharedMemory}. This can be useful when shared memory is passed as
+       file descriptor through JNI or binder service implemented in cpp.
+     * <p> Note that newly created {@code SharedMemory} takes ownership of passed {@code fd} and
+     * the original {@code fd} becomes detached (Check {@link ParcelFileDescriptor#detachFd()}).
+     * If the caller wants to use the file descriptor after the call, the caller should duplicate
+     * the file descriptor (Check {@link ParcelFileDescriptor#dup()}) and pass the duped version
+     * instead.
+     *
+     * @param fd File descriptor of shared memory passed as {@link ParcelFileDescriptor}.
+     */
+    public static @NonNull SharedMemory fromFileDescriptor(@NonNull ParcelFileDescriptor fd) {
+        FileDescriptor f = new FileDescriptor();
+        f.setInt$(fd.detachFd());
+        return new SharedMemory(f);
+    }
+
     private static final int PROT_MASK = OsConstants.PROT_READ | OsConstants.PROT_WRITE
             | OsConstants.PROT_EXEC | OsConstants.PROT_NONE;