Mark some http/tests/inspector/resource-tree as slow, unflake others.

third_party/WebKit/LayoutTests/http/tests/inspector/resource-tree/resource-request-content-while-loading.html

Index: third_party/WebKit/LayoutTests/http/tests/inspector/resource-tree/resource-request-content-while-loading.html
diff --git a/third_party/WebKit/LayoutTests/http/tests/inspector/resource-tree/resource-request-content-while-loading.html b/third_party/WebKit/LayoutTests/http/tests/inspector/resource-tree/resource-request-content-while-loading.html
index ad3140deed655ef5c16d4b262b28d60b3674c339..d8ef4de55ba13f53601a4c2fd25112abe0003392 100644
--- a/third_party/WebKit/LayoutTests/http/tests/inspector/resource-tree/resource-request-content-while-loading.html
+++ b/third_party/WebKit/LayoutTests/http/tests/inspector/resource-tree/resource-request-content-while-loading.html
@@ -25,15 +25,20 @@ function test()
         if (request.url.indexOf("styles-initial") === -1)
             return;
         resource = InspectorTest.resourceMatchingURL("styles-initial");
-        if (!resource || !resource.request || contentWasRequested)
-            return;
+        if (!resource || !resource.request || contentWasRequested) {
+            InspectorTest.addResult("Cannot find resource");
+            InspectorTest.completeTest();
+        }
         resource.requestContent(contentLoaded);
         contentWasRequested = true;
     }
 
     function pageAgentGetResourceContentCalled()
     {
-        InspectorTest.assertTrue(resource.request.finished);
+        if (!resource.request.finished) {
+            InspectorTest.addResult("Request must be finished before calling getResourceContent");
+            InspectorTest.completeTest();
+        }
     }
 
     function contentLoaded(content)