Revert of [DevTools] Show sync XHR info during request loading.

Revert of [DevTools] Show sync XHR info during request loading. (patchset #2 id:20001 of https://codereview.chromium.org/1183173002/)

Reason for revert:
Caused crashes to several inspector tests:
https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20MSAN/builds/3753

  http/tests/inspector/filesystem/async-callstack-filesystem.html [ Crash ]
  http/tests/inspector/filesystem/request-file-content.html [ Crash ]
  http/tests/inspector/service-workers/service-workers-view.html [ Crash ]
  http/tests/inspector/service-workers/user-agent-override.html [ Crash ]
  inspector/console/console-revoke-error-in-worker.html [ Crash ]
  inspector/console/console-uncaught-promise-in-worker.html [ Crash ]
  inspector/console/worker-eval-contains-stack.html [ Crash ]
  inspector/console/worker-exception-message-contains-stack.html [ Crash ]
  inspector/file-reader-with-network-panel.html [ Crash ]
  inspector/sources/debugger-ui/script-snippet-model.html [ Crash ]

==4==WARNING: MemorySanitizer: use-of-uninitialized-value
      #0 0x7fed2e08e7c3 in blink::InspectorResourceAgent::documentThreadableLoaderStartedLoadingForClient(unsigned long, blink::ThreadableLoaderClient*) third_party/WebKit/Source/core/inspector/InspectorResourceAgent.cpp:496:9
      #1 0x7fed2e1aabae in documentThreadableLoaderStartedLoadingForClient /b/build/slave/WebKit_Linux_MSAN/build/src/out/Release/gen/blink/core/InspectorInstrumentationInl.h:598:9
      #2 0x7fed2e1aabae in blink::DocumentThreadableLoader::loadRequest(blink::ResourceRequest const&, blink::ResourceLoaderOptions) third_party/WebKit/Source/core/loader/DocumentThreadableLoader.cpp:593:0


Original issue's description:
> [DevTools] Show sync XHR info during request loading.
> 
> BUG=500219
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197128

TBR=pfeldman@chromium.org,dgozman@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=500219
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197138

[jianli, 2015-06-15 21:13:32]

Created Revert of [DevTools] Show sync XHR info during request loading.

[commit-bot: I haz the power, 2015-06-15 21:13:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1175263003/1

[commit-bot: I haz the power, 2015-06-15 21:14:29]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197138