tcmalloc: Make some tcmalloc constants truly const.

Original CL:

- https://chromium-review.googlesource.com/c/chromium/src/+/777963

  Make some tcmalloc constants truly const.

  Change-Id: I84e036d5c71373ce3572d4b67b06fcadb25bb347
  Reviewed-on: https://chromium-review.googlesource.com/777963
  Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
  Cr-Commit-Position: refs/heads/master@{#517642}

BUG=724399,b:70905156

Change-Id: I21e732e8001eeea57b7fea95cc9ec6df21f12dea
Reviewed-on: https://chromium-review.googlesource.com/c/1130809Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Gabriel Marin <gmx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597329}

third_party/tcmalloc/chromium/src/tcmalloc.cc

@@ -936,13 +936,13 @@ class TCMallocImplementation : public MallocExtension {
   }
 
   virtual void GetFreeListSizes(vector<MallocExtension::FreeListInfo>* v) {
-    static const char* kCentralCacheType = "tcmalloc.central";
-    static const char* kTransferCacheType = "tcmalloc.transfer";
-    static const char* kThreadCacheType = "tcmalloc.thread";
-    static const char* kPageHeapType = "tcmalloc.page";
-    static const char* kPageHeapUnmappedType = "tcmalloc.page_unmapped";
-    static const char* kLargeSpanType = "tcmalloc.large";
-    static const char* kLargeUnmappedSpanType = "tcmalloc.large_unmapped";
+    static const char kCentralCacheType[] = "tcmalloc.central";
+    static const char kTransferCacheType[] = "tcmalloc.transfer";
+    static const char kThreadCacheType[] = "tcmalloc.thread";
+    static const char kPageHeapType[] = "tcmalloc.page";
+    static const char kPageHeapUnmappedType[] = "tcmalloc.page_unmapped";
+    static const char kLargeSpanType[] = "tcmalloc.large";
+    static const char kLargeUnmappedSpanType[] = "tcmalloc.large_unmapped";
 
     v->clear();