Bug 1580352 - Avoid potential undefined behavior (left-shifting a negative integer) in pixman. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D45512

--HG--
extra : moz-landing-system : lando

gfx/cairo/libpixman/src/pixman.h

@@ -132,7 +132,7 @@ typedef pixman_fixed_16_16_t	pixman_fixed_t;
 #define pixman_fixed_1_minus_e		(pixman_fixed_1 - pixman_fixed_e)
 #define pixman_fixed_minus_1		(pixman_int_to_fixed(-1))
 #define pixman_fixed_to_int(f)		((int) ((f) >> 16))
-#define pixman_int_to_fixed(i)		((pixman_fixed_t) ((i) << 16))
+#define pixman_int_to_fixed(i)		((pixman_fixed_t) ((uint32_t)(i) << 16))
 #define pixman_fixed_to_double(f)	(double) ((f) / (double) pixman_fixed_1)
 #define pixman_double_to_fixed(d)	((pixman_fixed_t) ((d) * 65536.0))
 #define pixman_fixed_frac(f)		((f) & pixman_fixed_1_minus_e)