GLInProcessContext must ensure whether CommandBuffer loses context.

GLInProcessContext must ensure whether CommandBuffer loses context.

GLInProcessContext plays a similar role to GpuCommandBufferStub in InProcess
mode. GpuCommandBufferStub always ensures whether CommandBuffer loses context via
GpuCommandBufferStub::MakeCurrent(). However, GLInProcessContextImpl does not
have the similar routine. So, when the context is lost,
GLInProcessContextImpl::PumpCommands() pushes ahead GpuScheduler::PutChanged()
although GpuCommandBufferStub stops to run the scheduler.

This patch makes GLInProcessContextImpl stop to run the scheduler if the context
is lost.

TEST=GLRendererTestSyncPoint.SignalSyncPointOnLostContext in cc_unittests
BUG=258007

Review URL: https://chromiumcodereview.appspot.com/18614006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@210776 0039d316-1c4b-4281-b951-d872f2087c98