Fix surfaceflinger on integer sanitized builds.

Refactors unsigned integer overflows in traverseInReverseZOrder
to fix integer overflow sanitized builds.

Test: Compiled and checked output from sanitizer.
Bug: 30969751
Change-Id: I46299e7044d360e35ca35a5448b34e4299a500b7
Merged-In: I46299e7044d360e35ca35a5448b34e4299a500b7
1 file changed