[heap-profiler] Allow intermediate sampling heap profile retrieval during recording.

The sampling heap profiles can now be retrieved without stopping
the profiler.

BUG=v8:6887

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I491206d0bafd7d4e198622117c12aab0057e6bc6
Reviewed-on: https://chromium-review.googlesource.com/749700Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49160}

src/inspector/js_protocol.json

@@ -1144,6 +1144,12 @@
                 "returns": [
                     { "name": "profile", "$ref": "SamplingHeapProfile", "description": "Recorded sampling heap profile." }
                 ]
+            },
+            {
+                "name": "getSamplingProfile",
+                "returns": [
+                    { "name": "profile", "$ref": "SamplingHeapProfile", "description": "Return the sampling profile being collected." }
+                ]
             }
         ],
         "events": [

src/inspector/v8-heap-profiler-agent-impl.cc

@@ -363,17 +363,24 @@ buildSampingHeapProfileNode(const v8::AllocationProfile::Node* node) {
 
 Response V8HeapProfilerAgentImpl::stopSampling(
     std::unique_ptr<protocol::HeapProfiler::SamplingHeapProfile>* profile) {
+  Response result = getSamplingProfile(profile);
+  if (result.isSuccess()) {
+    m_isolate->GetHeapProfiler()->StopSamplingHeapProfiler();
+    m_state->setBoolean(HeapProfilerAgentState::samplingHeapProfilerEnabled,
+                        false);
+  }
+  return result;
+}
+
+Response V8HeapProfilerAgentImpl::getSamplingProfile(
+    std::unique_ptr<protocol::HeapProfiler::SamplingHeapProfile>* profile) {
   v8::HeapProfiler* profiler = m_isolate->GetHeapProfiler();
-  if (!profiler) return Response::Error("Cannot access v8 heap profiler");
   v8::HandleScope scope(
-      m_isolate);  // Allocation profile contains Local handles.
+      m_isolate);  // v8::AllocationProfile contains Local handles.
   std::unique_ptr<v8::AllocationProfile> v8Profile(
       profiler->GetAllocationProfile());
-  profiler->StopSamplingHeapProfiler();
-  m_state->setBoolean(HeapProfilerAgentState::samplingHeapProfilerEnabled,
-                      false);
   if (!v8Profile)
-    return Response::Error("Cannot access v8 sampled heap profile.");
+    return Response::Error("V8 sampling heap profiler was not started.");
   v8::AllocationProfile::Node* root = v8Profile->GetRootNode();
   *profile = protocol::HeapProfiler::SamplingHeapProfile::create()
                  .setHead(buildSampingHeapProfileNode(root))

src/inspector/v8-heap-profiler-agent-impl.h

@@ -46,6 +46,8 @@ class V8HeapProfilerAgentImpl : public protocol::HeapProfiler::Backend {
   Response startSampling(Maybe<double> samplingInterval) override;
   Response stopSampling(
       std::unique_ptr<protocol::HeapProfiler::SamplingHeapProfile>*) override;
+  Response getSamplingProfile(
+      std::unique_ptr<protocol::HeapProfiler::SamplingHeapProfile>*) override;
 
  private:
   void startTrackingHeapObjectsInternal(bool trackAllocations);

test/inspector/heap-profiler/sampling-heap-profiler-expected.txt

+Checks sampling heap profiler methods.
+Expected error: V8 sampling heap profiler was not started.
+Allocated size is zero in the beginning: true
+Allocated size is more than 100KB after a chunk is allocated: true
+Allocated size increased after one more chunk is allocated: true
+Allocated size did not change after stopping: true
+Successfully finished

test/inspector/heap-profiler/sampling-heap-profiler.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --sampling-heap-profiler-suppress-randomness
+
+(async function() {
+  let {contextGroup, Protocol} = InspectorTest.start('Checks sampling heap profiler methods.');
+
+  contextGroup.addScript(`
+    var holder = [];
+    function allocateChunk() {
+      holder.push(new Array(100000).fill(42));
+    }
+    //# sourceURL=test.js`);
+
+  Protocol.HeapProfiler.enable();
+
+  const profile0 = await Protocol.HeapProfiler.getSamplingProfile();
+  InspectorTest.log('Expected error: ' + profile0.error.message);
+
+  await Protocol.HeapProfiler.startSampling();
+  const profile1 = await Protocol.HeapProfiler.getSamplingProfile();
+  const size1 = nodeSize(profile1.result.profile.head);
+  InspectorTest.log('Allocated size is zero in the beginning:', size1 === 0);
+
+  await Protocol.Runtime.evaluate({ expression: 'allocateChunk()' });
+  const profile2 = await Protocol.HeapProfiler.getSamplingProfile();
+  const size2 = nodeSize(profile2.result.profile.head);
+  InspectorTest.log('Allocated size is more than 100KB after a chunk is allocated:', size2 > 100000);
+
+  await Protocol.Runtime.evaluate({ expression: 'allocateChunk()' });
+  const profile3 = await Protocol.HeapProfiler.getSamplingProfile();
+  const size3 = nodeSize(profile3.result.profile.head);
+  InspectorTest.log('Allocated size increased after one more chunk is allocated:', size3 > size2);
+
+  const profile4 = await Protocol.HeapProfiler.stopSampling();
+  const size4 = nodeSize(profile4.result.profile.head);
+  InspectorTest.log('Allocated size did not change after stopping:', size4 === size3);
+
+  InspectorTest.log('Successfully finished');
+  InspectorTest.completeTest();
+
+  function nodeSize(node) {
+    return node.children.reduce((res, child) => res + nodeSize(child),
+                                node.callFrame.functionName === 'allocateChunk' ? node.selfSize : 0);
+  }
+})();