Revert "Disable flaky chromedriver test"

This reverts commit 49c25ee7.

Reason for revert: The original CL doesn't have the desired effects.

Original change's description:
> Disable flaky chromedriver test
> 
> Disable the following test:
> SessionHandlingTest.testGetSessions
> SessionHandlingTest.testQuitASessionMoreThanOnce
> SupportIPv4AndIPv6.testSupportIPv4AndIPv6
> ZChromeStartRetryCountTest.testChromeStartRetryCount
> 
> Bug: 899919
> Change-Id: I4fdebcce8d0784f4a03d740fe75cad489e7cc2f1
> Tbr: johnchen@chromium.org
> Reviewed-on: https://chromium-review.googlesource.com/c/1307594
> Reviewed-by: Owen Min <zmin@chromium.org>
> Commit-Queue: Owen Min <zmin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#603893}

TBR=zmin@chromium.org,johnchen@chromium.org

Change-Id: Ia4d948632cb8141de5a8214569432e066ab7ab90
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 899919
Reviewed-on: https://chromium-review.googlesource.com/c/1308655Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603981}

chrome/test/chromedriver/test/test_expectations

@@ -30,18 +30,8 @@ _REVISION_NEGATIVE_FILTER['HEAD'] = [
 
 _OS_NEGATIVE_FILTER = {}
 _OS_NEGATIVE_FILTER['win'] = [
-    # https://crbug.com/899919
-    'SessionHandlingTest.testGetSessions',
-    'SessionHandlingTest.testQuitASessionMoreThanOnce',
-    'SupportIPv4AndIPv6.testSupportIPv4AndIPv6',
-    'ZChromeStartRetryCountTest.testChromeStartRetryCount',
 ]
 _OS_NEGATIVE_FILTER['linux'] = [
-    # https://crbug.com/899919
-    'SessionHandlingTest.testGetSessions',
-    'SessionHandlingTest.testQuitASessionMoreThanOnce',
-    'SupportIPv4AndIPv6.testSupportIPv4AndIPv6',
-    'ZChromeStartRetryCountTest.testChromeStartRetryCount',
 ]
 _OS_NEGATIVE_FILTER['mac'] = [
     # https://crbug.com/868599
@@ -49,12 +39,6 @@ _OS_NEGATIVE_FILTER['mac'] = [
     'WindowTest.testCanMaximizeTheWindowFromIframe',
     'WindowTest.testSetsTheSizeOfTheCurrentWindow',
     'WindowTest.testCanMaximizeTheWindow',
-
-    # https://crbug.com/899919
-    'SessionHandlingTest.testGetSessions',
-    'SessionHandlingTest.testQuitASessionMoreThanOnce',
-    'SupportIPv4AndIPv6.testSupportIPv4AndIPv6',
-    'ZChromeStartRetryCountTest.testChromeStartRetryCount',
 ]
 
 _SPECIFIC_OS_REVISION_NEGATIVE_FILTER = {}