RPP: add getMainThreadActivity function to Insights AI

This CL enables the LLM to query for relevant main thread activity for
the given insight.

Note that we may need to experiment with alternative versions of this
that are leaner in order to avoid eating up context windows, but this is
a good starting point.

Bug: 394552594
Change-Id: I2017f190f783743f813abea57e9dfca92c9f6855
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6275957
Auto-Submit: Jack Franklin <[email protected]>
Reviewed-by: Alex Rudenko <[email protected]>
Commit-Queue: Jack Franklin <[email protected]>

Author: jackfranklin

front_end/panels/ai_assistance/agents/PerformanceInsightsAgent.test.ts

@@ -131,5 +131,30 @@ What is this?`;
       assert.deepEqual(
           action, {type: 'action' as ActionResponse['type'], output: expectedOutput, code: undefined, canceled: false});
     });
+
+    it('calls getMainThreadActivity', async function() {
+      const {parsedTrace, insights} = await TraceLoader.traceEngine(this, 'lcp-discovery-delay.json.gz');
+      assert.isOk(insights);
+      const [firstNav] = parsedTrace.Meta.mainFrameNavigations;
+      const lcpPhases = getInsightOrError('LCPPhases', insights, firstNav);
+      const agent = new PerformanceInsightsAgent({
+        aidaClient: mockAidaClient(
+            [[{explanation: '', functionCalls: [{name: 'getMainThreadActivity', args: {}}]}], [{explanation: 'done'}]])
+      });
+      const activeInsight = new TimelineUtils.InsightAIContext.ActiveInsight(lcpPhases, parsedTrace);
+      const context = new InsightContext(activeInsight);
+
+      const responses = await Array.fromAsync(agent.run('test', {selected: context}));
+      const action = responses.find(response => response.type === ResponseType.ACTION);
+
+      const expectedTree = TimelineUtils.InsightAIContext.AIQueries.mainThreadActivity(lcpPhases, parsedTrace);
+      assert.isOk(expectedTree);
+
+      const expectedOutput = JSON.stringify({activity: expectedTree.serialize()});
+
+      assert.exists(action);
+      assert.deepEqual(
+          action, {type: 'action' as ActionResponse['type'], output: expectedOutput, code: undefined, canceled: false});
+    });
   });
 });

front_end/panels/ai_assistance/agents/PerformanceInsightsAgent.ts

@@ -135,6 +135,51 @@ export class PerformanceInsightsAgent extends AiAgent<TimelineUtils.InsightAICon
         return {result: {requests: formatted}};
       },
     });
+
+    this.declareFunction<Record<never, unknown>, {activity: string}>('getMainThreadActivity', {
+      description: `Returns the main thread activity for the selected insight.
+The tree is represented as a call frame with a root task and a series of children.
+The format of each callframe is:
+
+    Node: $id – $name
+    Selected: true
+    dur: $duration
+    self: $self
+    URL #: $url_number
+    Children:
+      * $child.id – $child.name
+
+The fields are:
+
+* name:  A short string naming the callframe (e.g. 'Evaluate Script' or the JS function name 'InitializeApp')
+* id:  A numerical identifier for the callframe
+* Selected:  Set to true if this callframe is the one the user selected.
+* url_number:  The number of the URL referenced in the "All URLs" list
+* dur:  The total duration of the callframe (includes time spent in its descendants), in milliseconds.
+* self:  The self duration of the callframe (excludes time spent in its descendants), in milliseconds. If omitted, assume the value is 0.
+* children:  An list of child callframes, each denoted by their id and name`,
+      parameters: {
+        type: Host.AidaClient.ParametersTypes.OBJECT,
+        description: '',
+        nullable: true,
+        properties: {},
+      },
+      handler: async () => {
+        if (!this.#insight) {
+          return {error: 'No insight available'};
+        }
+        const activeInsight = this.#insight.getItem();
+        const tree = TimelineUtils.InsightAIContext.AIQueries.mainThreadActivity(
+            activeInsight.insight,
+            activeInsight.parsedTrace,
+        );
+        if (!tree) {
+          return {error: 'No main thread activity found'};
+        }
+        return {result: {activity: tree.serialize()}};
+      },
+
+    });
   }
 
   override async enhanceQuery(