Only enable heap tracking under --enable-heap-profiling=task-profiler.

BUG=692045

Review-Url: https://codereview.chromium.org/2695013005
Cr-Commit-Position: refs/heads/master@{#450984}
diff --git a/base/base_switches.h b/base/base_switches.h
index 0585186..04b0773 100644
--- a/base/base_switches.h
+++ b/base/base_switches.h
@@ -16,6 +16,7 @@
 extern const char kEnableCrashReporter[];
 extern const char kEnableHeapProfiling[];
 extern const char kEnableHeapProfilingModeNative[];
+extern const char kEnableHeapProfilingTaskProfiler[];
 extern const char kEnableLowEndDeviceMode[];
 extern const char kForceFieldTrials[];
 extern const char kFullMemoryCrashReport[];