Fix compile warning [-Wtype-limits]

This fixes warning on android_arm build.
Previously the compiler complained about a check that can never be true.
See second check below(index is size_t type, FIRST_SPACE=0):
if (index > i::LAST_SPACE || index < i::FIRST_SPACE)
And make the code easy to understand.

BUG=

Review URL: https://codereview.chromium.org/1155043005

Cr-Commit-Position: refs/heads/master@{#29042}

src/api.cc

@@ -7273,9 +7273,8 @@ size_t Isolate::NumberOfHeapSpaces() {
 
 bool Isolate::GetHeapSpaceStatistics(HeapSpaceStatistics* space_statistics,
                                      size_t index) {
-  if (!space_statistics)
-    return false;
-  if (index > i::LAST_SPACE || index < i::FIRST_SPACE)
+  if (!space_statistics) return false;
+  if (!i::Heap::IsValidAllocationSpace(static_cast<i::AllocationSpace>(index)))
     return false;
 
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);

src/heap/heap.cc

@@ -5019,6 +5019,20 @@ bool Heap::InSpace(Address addr, AllocationSpace space) {
 }
 
 
+bool Heap::IsValidAllocationSpace(AllocationSpace space) {
+  switch (space) {
+    case NEW_SPACE:
+    case OLD_SPACE:
+    case CODE_SPACE:
+    case MAP_SPACE:
+    case LO_SPACE:
+      return true;
+    default:
+      return false;
+  }
+}
+
+
 bool Heap::RootIsImmortalImmovable(int root_index) {
   switch (root_index) {
 #define CASE(name)               \

src/heap/heap.h

@@ -955,6 +955,9 @@ class Heap {
   bool InSpace(Address addr, AllocationSpace space);
   bool InSpace(HeapObject* value, AllocationSpace space);
 
+  // Checks whether the space is valid.
+  static bool IsValidAllocationSpace(AllocationSpace space);
+
   // Checks whether the given object is allowed to be migrated from it's
   // current space into the given destination space. Used for debugging.
   inline bool AllowedToBeMigrated(HeapObject* object, AllocationSpace dest);