Add support for the PointerLocation overlay.

This change involves adding a new method to IWindowManager,
monitorInput() that returns an InputChannel to receive a copy of all
input that is dispatched to applications.  The caller must have
the READ_INPUT_STATE permission to make this request (similar to
other window manager methods such as getKeycodeState).

Change-Id: Icd14d810174a5b2928671ef16de73af88302aea0

include/utils/String8.h

@@ -171,7 +171,8 @@ public:
             status_t            append(const char* other);
             status_t            append(const char* other, size_t numChars);
 
-            status_t            appendFormat(const char* fmt, ...);
+            status_t            appendFormat(const char* fmt, ...)
+                    __attribute__((format (printf, 2, 3)));
 
             // Note that this function takes O(N) time to calculate the value.
             // No cache value is stored.