Split apart TabLoader::ForceLoadTimerFired DCHECK.

A recent albatross build is showing that this DCHECK is firing. Splitting apart
the DCHECK will allow diagnosing which condition is failing.

BUG=895520

Change-Id: I4dcb6a819b308ab407666c81b90536b8fcfef7cb
Reviewed-on: https://chromium-review.googlesource.com/c/1282728Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599942}

chrome/browser/sessions/tab_loader.cc

@@ -464,10 +464,11 @@ void TabLoader::ForceLoadTimerFired() {
   ReentrancyHelper lifetime_helper(this);
 
   // CheckInvariants can't be called directly as the timer is no longer
-  // running at this point. However, the condition under which the timer
+  // running at this point. However, the conditions under which the timer
   // should be running can be checked.
-  DCHECK(is_loading_enabled_ && !tabs_to_load_.empty() &&
-         !tabs_loading_.empty());
+  DCHECK(is_loading_enabled_);
+  DCHECK(!tabs_to_load_.empty());
+  DCHECK(!tabs_loading_.empty());
   DCHECK(!force_load_time_.is_null());
 
   // A timeout is in some sense equivalent to a "load" event, in that it means