Revert 230444 "content: Disable CommandBufferProxyImpl::Flush tr..."

> content: Disable CommandBufferProxyImpl::Flush traces by default.
> 
> BUG=309441
> 
> Review URL: https://codereview.chromium.org/33003003

The number of command buffer flushes with impl-side painting should
now have been reduced to an amount that allows us to have these
traces enabled by default.

TBR=piman@chromium.org
BUG=309441

Review URL: https://codereview.chromium.org/62093002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233293 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233293