[heap] Update verification of LO_SPACE in SizeOfInitialHeap

On PPC64 linux the OS page size is 64KB, therefore when the
snapshot is created the serialized heap already has LO_SPACE
allocated(the allocation goes beyond the 1st page of
CODE_SPACE and hence LO_SPACE is allocated).
I've updated the testcase to check if the delta
of the LO_SPACE is zero.

R=mlippautz@chromium.org, ulan@chromium.org, vogelheim@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2394893002
Cr-Commit-Position: refs/heads/master@{#40014}

test/cctest/heap/test-spaces.cc

@@ -500,6 +500,8 @@ TEST(SizeOfInitialHeap) {
            ->IsUndefined()) {
     return;
   }
+  // Initial size of LO_SPACE
+  size_t initial_lo_space = isolate->heap()->lo_space()->Size();
 
   // The limit for each space for an empty isolate containing just the
   // snapshot.
@@ -528,7 +530,7 @@ TEST(SizeOfInitialHeap) {
   }
 
   // No large objects required to perform the above steps.
-  CHECK(isolate->heap()->lo_space()->IsEmpty());
+  CHECK_EQ(initial_lo_space, isolate->heap()->lo_space()->Size());
 }
 
 static HeapObject* AllocateUnaligned(NewSpace* space, int size) {