[heap] Add missing spaces between scavenge trace categories.

Bug: 
Change-Id: I780c83686b741e4d63a49ccb119a920c817d5a0a
Reviewed-on: https://chromium-review.googlesource.com/704718Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48342}

src/heap/gc-tracer.cc

@@ -462,8 +462,8 @@ void GCTracer::PrintNVP() const {
           "scavenge=%.2f "
           "scavenge.roots=%.2f "
           "scavenge.weak=%.2f "
-          "scavenge.weak_global_handles.identify=%.2f"
-          "scavenge.weak_global_handles.process=%.2f"
+          "scavenge.weak_global_handles.identify=%.2f "
+          "scavenge.weak_global_handles.process=%.2f "
           "scavenge.parallel=%.2f "
           "incremental.steps_count=%d "
           "incremental.steps_took=%.1f "