[Telemetry] Expose v8's window.gc() method to the PerfTestRunner.

Blink's PerfTestRunner has a gc method which tries to call
window.GCController.collect(), if it doesn't exist, it allocates a whole
bunch of memory to try to trigger a gc.

Since the blink_perf Measurement already passes --js-flags=--expose_gc,
we can call the window.gc() method instead of this hackery.

I'm hopeful that this will fix the Bindings/gc-tree.html crashes on
android.

BUG=252897
R=dtu@chromium.org

Review URL: https://codereview.chromium.org/17472007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@207975 0039d316-1c4b-4281-b951-d872f2087c98

tools/perf/perf_tools/blink_perf.js

@@ -11,4 +11,10 @@ testRunner.dumpAsText = function() {};
 testRunner.notifyDone = function() {
   this.isDone = true;
 };
+
+window.GCController = {};
+
+GCController.collect = function() {
+  gc();
+};
 })();