browser_tests hangs with drcov tool on Linux

_From [zhao...@google.com](https://code.google.com/u/106321947286816917100/) on March 13, 2014 17:05:33_

/home/zhaoqin/Workspace/DynamoRIO/builds/build_x64_dbg.git/bin64/drrun -debug -checklevel 1 -disable_traces -c /home/zhaoqin/Workspace/DynamoRIO/builds/build_x64_dbg.git/clients/lib64/debug/libdrcov.so -- ./out/Release/browser_tests --no-sandbox --gtest_filter=AppListStartPageWebUITest.Basic --ui-test-action-max-timeout=80000000 --ui-test-action-timeout=40000000

> ps -U zhaoqin | grep brow
7990 pts/11 00:20:53 browser_tests
8022 pts/11 00:21:02 browser_tests
9451 pts/11 00:00:01 browser_tests
9453 pts/11 00:00:18 browser_tests
9454 pts/11 00:00:00 browser_tests
9455 pts/11 00:00:01 browser_tests
9490 pts/11 00:05:06 browser_tests
9510 pts/11 00:05:14 browser_tests

Attach to 9451, 9453, stop at nop after syscall
Attach to 9490, 9510, loop at debug_infinite_loop

It runs fine without drcov client

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1390_