Explicitly set swap memory metrics to zero on Fuchsia

Bug: 750948
Test: CQ
Change-Id: Ic11aec698c70d8d562ab51c16859b248b430b0f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2299620
Commit-Queue: Gabriel Kerneis <kerneis@google.com>
Commit-Queue: Primiano Tucci <primiano@chromium.org>
Auto-Submit: Gabriel Kerneis <kerneis@google.com>
Reviewed-by: Primiano Tucci <primiano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788560}

services/resource_coordinator/public/cpp/memory_instrumentation/os_metrics.h

@@ -20,11 +20,14 @@ FORWARD_DECLARE_TEST(ProfilingJsonExporterTest, MemoryMaps);
 namespace memory_instrumentation {
 
 // This class provides synchronous access to memory metrics for a process with a
-// given |pid|. These interfaces have platform-specific restrictrions:
+// given |pid|. These interfaces have platform-specific restrictions:
 //  * On Android, due to sandboxing restrictions, processes can only access
 //    memory metrics for themselves. Thus |pid| must be equal to getpid().
 //  * On Linux, due to sandboxing restrictions, only the privileged browser
 //    process has access to memory metrics for sandboxed child processes.
+//  * On Fuchsia, due to the API expecting a ProcessId rather than a
+//    ProcessHandle, processes can only access memory metrics for themselves or
+//    for children of base::GetDefaultJob().
 //
 // These restrictions mean that any code that wishes to be cross-platform
 // compatible cannot synchronously obtain memory metrics for a |pid|. Instead,

services/resource_coordinator/public/cpp/memory_instrumentation/os_metrics_fuchsia.cc

@@ -36,6 +36,8 @@ bool OSMetrics::FillOSMemoryDump(base::ProcessId pid,
 
   dump->resident_set_kb = rss_bytes / 1024;
   dump->platform_private_footprint->rss_anon_bytes = rss_anon_bytes;
+  // Fuchsia has no swap.
+  dump->platform_private_footprint->vm_swap_bytes = 0;
   return true;
 }