tcmalloc: Don't let tcmalloc read all kinds of env vars at startup.

Original CL:

- https://codereview.chromium.org/281613004

  Don't let tcmalloc read all kinds of env vars at startup.

  The env vars are still used in profiling=1 builds, by such illustrious
  figures as the deep memory profiler bot and willchan. Reading from the
  environment variables uses static initializers, so this change will
  eliminate those static initializers in profiling=0 builds.

  As discussed in the chromium-dev thread "Does anyone use tcmalloc's
  debugging envvars?".

  BUG=94925
  NOTRY=true

BUG=724399,b:70905156

Change-Id: Ic143dfca456a3475be0938af53c0eb4308f457d1
Reviewed-on: https://chromium-review.googlesource.com/1130780Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Gabriel Marin <gmx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579496}

third_party/tcmalloc/chromium/src/base/commandlineflags.h

@@ -157,6 +157,8 @@ namespace tcmalloc {
 // These macros (could be functions, but I don't want to bother with a .cc
 // file), make it easier to initialize flags from the environment.
 
+#if defined(ENABLE_PROFILING)
+
 #define EnvToString(envname, dflt)   \
   (!getenv(envname) ? (dflt) : getenv(envname))
 
@@ -172,4 +174,14 @@ namespace tcmalloc {
 #define EnvToDouble(envname, dflt)  \
   tcmalloc::commandlineflags::StringToDouble(getenv(envname), dflt)
 
+#else  // defined(ENABLE_PROFILING)
+
+#define EnvToString(envname, dflt) (dflt)
+#define EnvToBool(envname, dflt) (dflt)
+#define EnvToInt(envname, dflt) (dflt)
+#define EnvToInt64(envname, dflt) (dflt)
+#define EnvToDouble(envname, dflt) (dflt)
+
+#endif  // defined(ENABLE_PROFILING)
+
 #endif  // BASE_COMMANDLINEFLAGS_H_