[Site Isolation] Implement Page.getResourceTree on the UIProcess ProxyingPageAgent

1c2a6d9

LayoutTests/http/tests/site-isolation/inspector/page/resource-tree-cross-origin-iframe.html

+let { frameTree } = await WI.backendTarget.PageAgent.getResourceTree();
+
+InspectorTest.expectEqual(child.frame.parentId, frameTree.frame.id, "Child frame's parentId should match main frame's id.");
+InspectorTest.expectEqual(child.frame.name, "child-frame", "Child frame's name attribute should be reported.");
+
+// FIXME: The inspectedPage's WebFrameProxy never observes the cross-origin
+// child's didCommitLoadForFrame, so url() and documentSecurityOriginData() remain stale.

WebKit Site Isolation places cross-origin iframes in separate WebContent processes. The UIProcess maintains a WebFrameProxy tree that aggregates frame identity across all of those processes. The ProxyingPageAgent is the UIProcess-side inspector agent that multiplexes the WebKit Inspector Protocol across WebContent processes; its backendTarget represents the aggregated web-page target visible to the frontend.

This commit implements Page.getResourceTree on the UIProcess ProxyingPageAgent by recursively walking WebFrameProxy::childFrames(), which spans every WebContent process. New frameName(), childFrames(), and a null-guarded documentSecurityOriginData() are added on WebFrameProxy. NetworkManager is guarded against clobbering the live per-page frame tree when the multiplexing backendTarget initializes. Critically, the UIProcess WebFrameProxy never receives didCommitLoadForFrame for cross-origin children — so the new walk returns correct structural data (frame IDs, parent linkage, name) but stale/wrong URL and security origin data for cross-origin frames, a gap the commit explicitly defers to follow-up bugs.

Before:                                  After:
  Inspector Frontend                       Inspector Frontend
    └─► per-page PageAgent.getResourceTree    └─► backendTarget ProxyingPageAgent.getResourceTree
          └─► WebContent A only                       └─► UIProcess WebFrameProxy tree
                (cross-origin: invisible)                   ├─► main frame [A]  url/origin: live
                                                            └─► cross-origin [B]  url/origin: STALE
                                                                  └─► grandchild [A]  ⚠ ID collision

Significance

This is the foundational step toward full inspector visibility across Site Isolation process boundaries — cross-origin child frames in remote processes were previously invisible to the inspector frontend. It also opens new UIProcess-side paths that touch security origin data, and the commit explicitly acknowledges that cross-origin URL and origin reporting remain stale and incomplete.

Audit directions

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🔒

Frame identity collisions and stale cross-origin origin data in this new inspector path have several audit-worthy edge cases.

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