Revert of Blink roll 178929:178934 (https://codereview.chromium.org/417113005/)

Reason for revert:
Seems to have broken browser_tests:
DevToolsSanityTest.TestNoScriptDuplicatesOnPanelSwitch (run #4):
[ RUN      ] DevToolsSanityTest.TestNoScriptDuplicatesOnPanelSwitch
HTTP server started on http://127.0.0.1:52329...
sending server_data: {"host": "127.0.0.1", "port": 52329} (36 bytes)
../../chrome/browser/devtools/devtools_sanity_browsertest.cc:104: Failure
Value of: result
  Actual: "[FAILED] TypeError: Cannot read property 'sourcesView' of undefined"
Expected: "[OK]"

Original issue's description:
> Blink roll 178929:178934
> 
> http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog_blink.html?url=/trunk&range=178930:178934&mode=html
> TBR=haraken@chromium.org,jchaffraix@chromium.org
> BUG=
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=285602

TBR=haraken@chromium.org,jchaffraix@chromium.org,blink-deps-roller@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/414223006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285622 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -28,7 +28,7 @@ vars = {
   "libcxxabi_revision": "206024",
   "webkit_trunk": "http://src.chromium.org/blink/trunk",
   "nacl_trunk": "http://src.chromium.org/native_client/trunk",
-  "webkit_revision": "178934",
+  "webkit_revision": "178929",
   "chromium_git": "https://chromium.googlesource.com",
   "chromiumos_git": "https://chromium.googlesource.com/chromiumos",
   "pdfium_git": "https://pdfium.googlesource.com",