Fix constant pool printing error

the size of constant pool should be constant_pool_offset to safepoint_offset

Bug: 
Change-Id: I2290ed49ccbeaa12706f2e7c37b72c96bec11fd3
Reviewed-on: https://chromium-review.googlesource.com/721960
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48702}

src/objects.cc

@@ -14466,7 +14466,7 @@ void Code::Disassemble(const char* name, std::ostream& os) {  // NOLINT
     Disassembler::Decode(isolate, &os, begin, end, this);
 
     if (constant_pool_offset < size) {
-      int constant_pool_size = size - constant_pool_offset;
+      int constant_pool_size = safepoint_offset - constant_pool_offset;
       DCHECK_EQ(constant_pool_size & kPointerAlignmentMask, 0);
       os << "\nConstant Pool (size = " << constant_pool_size << ")\n";
       Vector<char> buf = Vector<char>::New(50);