Initial implementation of performance.measureMemory API

This adds IDL files and an experimental feature flag for the API.
The implementation simply forwards to v8::Isolate::MeasureMemory.

Bug: 973627

Change-Id: I80ac8b78e81a6fad6b25370b419a0392f6589cee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1796364
Reviewed-by: Yoav Weiss <[email protected]>
Reviewed-by: Kentaro Hara <[email protected]>
Commit-Queue: Ulan Degenbaev <[email protected]>
Cr-Commit-Position: refs/heads/master@{#703262}

Author: ulan

measure-memory/META.yml

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+suggested_reviewers:
+  - ulan

measure-memory/README.md

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+# Tentative tests for performance.measureMemory API
+
+Tests in this directory are for the proposed performance.measureMemory API.
+This is not yet standardised and browsers should not be expected to pass
+these tests.
+
+See the explainer at
+https://github.com/ulan/javascript-agent-memory/blob/master/explainer.md
+for more information about the API.

measure-memory/measure-memory.tentative.any.js

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+function checkMeasureMemoryResultSummary(result) {
+    assert_own_property(result, "total");
+    assert_own_property(result.total, "jsMemoryEstimate");
+    assert_own_property(result.total, "jsMemoryRange");
+    assert_equals(result.total.jsMemoryRange.length, 2);
+    assert_greater_than_equal(
+        result.total.jsMemoryRange[1],
+        result.total.jsMemoryRange[0]);
+    assert_greater_than_equal(
+        result.total.jsMemoryEstimate,
+        result.total.jsMemoryRange[0]);
+    assert_greater_than_equal(
+        result.total.jsMemoryRange[1],
+        result.total.jsMemoryEstimate);
+}
+
+promise_test(async testCase => {
+  let result = await performance.measureMemory();
+  checkMeasureMemoryResultSummary(result);
+}, 'Well-formed result of performance.measureMemory with default arguments.');
+
+promise_test(async testcase => {
+  let result = await performance.measureMemory({detailed: false});
+  checkMeasureMemoryResultSummary(result);
+}, 'well-formed result of performance.measurememory with detailed=false.');