ThrottlingController::Liveness needs to be uint32_t

We are setting kAlive and kDead values assigning values that
are bigger than the maximum signed int32. It is better to use
uint32_t in this case.

Bug: 819294
Change-Id: If72b48291a66a3a9db24b4c8e2d11d31936a66ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1645772Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: José Dapena Paz <jose.dapena@lge.com>
Cr-Commit-Position: refs/heads/master@{#666619}

services/network/throttling/throttling_controller.h

@@ -38,7 +38,7 @@ class COMPONENT_EXPORT(NETWORK_SERVICE) ThrottlingController {
 
   // TODO(https://crbug.com/960874): Debugging code to try and shed some light
   // on why the owned maps are invalid.
-  enum class Liveness : int32_t {
+  enum class Liveness : uint32_t {
     kAlive = 0xCA11AB13,
     kDead = 0xDEADBEEF,
   };