Refine base::CommandLine suppression.

The base::CommandLine was overly broad. The flakiness analysis of
https://chromium-review.googlesource.com/c/chromium/src/+/1539787
reported that DumpAccessibilityTreeTest.AccessibilityObject and
QuicAllowedPolicyIsNotSet.NoQuicRegulations were flaky.

The latter has a 1.8% confidence and is on a non-TSan builder, so it's
probably a false positive. DumpAccessibilityTreeTest.AccessibilityObject
is real and is tracked in crbug/946481. Refine the suppression to just
cover that.

(If other command-line races come up, I think it's preferable to add new
suppressions and file new bugs rather than revive the overbroad
base::CommandLine suppression. The overbroad one has let new bugs
through, like the accessibility test.)

Bug: 946481, 334140
Change-Id: If09cb2fa2629751367e3fd822e3ba5159d529492
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1548138
Commit-Queue: David Benjamin <davidben@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Auto-Submit: David Benjamin <davidben@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646493}

build/sanitizers/tsan_suppressions.cc

@@ -121,11 +121,6 @@ char kTSanDefaultSuppressions[] =
     "race:content::"
     "VideoCaptureImplTest::MockVideoCaptureImpl::~MockVideoCaptureImpl\n"
 
-    // http://crbug.com/334140
-    "race:CommandLine::HasSwitch\n"
-    "race:CommandLine::current_process_commandline_\n"
-    "race:CommandLine::GetSwitchValueASCII\n"
-
     // http://crbug.com/347534
     "race:v8::internal::V8::TearDown\n"
 
@@ -209,6 +204,9 @@ char kTSanDefaultSuppressions[] =
     // http://crbug.com/797998
     "race:content::SandboxIPCHandler::HandleLocaltime\n"
 
+    // https://crbug.com/946481
+    "race:content::DumpAccessibilityTestBase::RunTestForPlatform\n"
+
     // End of suppressions.
     ;  // Please keep this semicolon.