Add MSE perf Telemetry tests.

tools/perf/page_sets/mse_cases.json

Index: tools/perf/page_sets/mse_cases.json
diff --git a/tools/perf/page_sets/mse_cases.json b/tools/perf/page_sets/mse_cases.json
new file mode 100644
index 0000000000000000000000000000000000000000..e355fbe6235dafa20db8d1adc7e7e9b3c9693330
--- /dev/null
+++ b/tools/perf/page_sets/mse_cases.json
@@ -0,0 +1,42 @@
+{
+  "description": "Media source extensions perf benchmark",
+  "media_metrics": {"action": "wait", "javascript" : "window.__testDone() == true"},
+  "pages": [
+    {
+      "url": "file://mse_cases/startup_test.html?testType=AV"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=AV&useAppendStream=true"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=AV&doNotWaitForBodyOnLoad=true"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=AV&useAppendStream=true&doNotWaitForBodyOnLoad=true"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=V"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=V&useAppendStream=true"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=V&doNotWaitForBodyOnLoad=true"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=V&useAppendStream=true&doNotWaitForBodyOnLoad=true"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=A"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=A&useAppendStream=true"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=A&doNotWaitForBodyOnLoad=true"
+    },
+    {
+      "url": "file://mse_cases/startup_test.html?testType=A&useAppendStream=true&doNotWaitForBodyOnLoad=true"
+    }
+  ]
+}