[heap] Use size_t for heap and space counters.

test/cctest/heap/test-spaces.cc

Index: test/cctest/heap/test-spaces.cc
diff --git a/test/cctest/heap/test-spaces.cc b/test/cctest/heap/test-spaces.cc
index 0f2083d56c7e3ed5fc376c44774d1313a61fe717..9a7585d68180dd2269cce67000747f1d723574eb 100644
--- a/test/cctest/heap/test-spaces.cc
+++ b/test/cctest/heap/test-spaces.cc
@@ -471,7 +471,7 @@ TEST(LargeObjectSpace) {
   CHECK(lo->Contains(ho));
 
   while (true) {
-    intptr_t available = lo->Available();
+    size_t available = lo->Available();
     { AllocationResult allocation = lo->AllocateRaw(lo_size, NOT_EXECUTABLE);
       if (allocation.IsRetry()) break;
     }