metrics: Add leak detector controller in Chrome OS metrics system

build/config/allocator.gni

Index: build/config/allocator.gni
diff --git a/build/config/allocator.gni b/build/config/allocator.gni
index 5b6d963d41cfb455c03dc95d61a350af94e6a268..b8f4fe7edb7448d62390e30671c0a63978b0bca2 100644
--- a/build/config/allocator.gni
+++ b/build/config/allocator.gni
@@ -14,6 +14,9 @@ if (is_android || current_cpu == "mipsel" || is_mac || is_ios || is_asan ||
 declare_args() {
   # Memory allocator to use. Set to "none" to use default allocator.
   use_allocator = _default_allocator
+
+  # Build runtime memory leak detector.
+  enable_leak_detector = false

[brettw, 2016/02/18 21:14:58]

This is still global in the sense that it's in the shared build directory. This
is used by different projects, including standalone V8. It doesn't apply to
non-Chrome projects.

Since this is a feature controlled by a component, the flag should also be in
that component. I'd add a new file
	components/metrics/leak_detector/leak_detector.gni and put this flag in a
declare_args block in there.

Can the documentation for this be more complete? This of this from the
perspective of somebody looking at this and wondering if they should turn it on.

[Simon Que, 2016/02/19 02:13:02]

Done.

 }
 
 assert(use_allocator == "none" || use_allocator == "tcmalloc")