Re-enable fixed viz_content_unittests

Some viz_content_unittests have been fixed, re-enabling them.

TBR=kylechar@chromium.org
TEST=RenderWidgetHostTest.FrameToken_RendererCrash,
     RenderWidgetHostTest.NewContentRenderingTimeout,
     RenderWidgetHostTest.SwapCompositorFrameWithBadSourceId

Bug: 760320
Change-Id: Ib52cd12d381575a134893d1d2d6f4b51021b4428
Reviewed-on: https://chromium-review.googlesource.com/943462Reviewed-by: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540167}

testing/buildbot/filters/viz.content_unittests.filter

 -RenderWidgetHostInputEventRouterTest.DoNotCoalesceGestureEvents
 -RenderWidgetHostInputEventRouterTest.DoNotCoalesceTouchEvents
--RenderWidgetHostTest.FrameToken_RendererCrash
--RenderWidgetHostTest.NewContentRenderingTimeout
--RenderWidgetHostTest.SwapCompositorFrameWithBadSourceId
 -RenderWidgetHostViewAuraSurfaceSynchronizationTest.CompositorFrameSinkChange
 -RenderWidgetHostViewAuraSurfaceSynchronizationTest.DiscardDelegatedFrames
 -RenderWidgetHostViewAuraSurfaceSynchronizationTest.DropFallbackWhenHidden