Create chrome_branch_deps.json for branch 6831.

Change-Id: I3d37d55f71c95c893ea918d03a71e613235a3008
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6009044
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/6831@{#1}
Cr-Branched-From: f40b7a7a-refs/heads/main@{#1380938}

chrome/chrome_branch_deps.json

+{
+  "src": "refs/branch-heads/6831",
+  "src:src/clank": "refs/heads/chromium/6831",
+  "src:src/components/optimization_guide/internal": "refs/heads/chromium/6831",
+  "src:src/internal": "refs/heads/chromium/6831",
+  "src:src/ios_internal": "refs/heads/chromium/6831",
+  "src:src/third_party/angle": "refs/heads/chromium/6831",
+  "src:src/third_party/dawn": "refs/heads/chromium/6831",
+  "src:src/third_party/devtools-frontend-internal": "refs/heads/chromium/6831",
+  "src:src/third_party/devtools-frontend-internal:devtools-frontend": "refs/heads/chromium/6831",
+  "src:src/third_party/devtools-frontend/src": "refs/heads/chromium/6831",
+  "src:src/third_party/instrumented_libs": "refs/heads/chromium/6831",
+  "src:src/third_party/openscreen/src": "refs/heads/chromium/6831",
+  "src:src/third_party/pdfium": "refs/heads/chromium/6831",
+  "src:src/third_party/vulkan-deps": "refs/heads/chromium/6831",
+  "src:src/third_party/webrtc": "refs/branch-heads/6831",
+  "src:src/v8": "refs/heads/chromium/6831"
+}