Add a gralloc usage flag for external displays.

This change adds a gralloc usage flag to indicate that a buffer should
be displayed full-screen on an external display if one is present.

Change-Id: I3230a8dd2c49c89c81bf0ee9e646a448028bda2e
diff --git a/include/hardware/gralloc.h b/include/hardware/gralloc.h
index 73cc9e0..788815a 100644
--- a/include/hardware/gralloc.h
+++ b/include/hardware/gralloc.h
@@ -70,6 +70,11 @@
     /* mask for the software usage bit-mask */
     GRALLOC_USAGE_HW_MASK         = 0x00001F00,
 
+    /* buffer should be displayed full-screen on an external display when
+     * possible
+     */
+    GRALLOC_USAGE_EXTERNAL_DISP   = 0x00002000,
+
     /* implementation-specific private usage flags */
     GRALLOC_USAGE_PRIVATE_0       = 0x10000000,
     GRALLOC_USAGE_PRIVATE_1       = 0x20000000,