Propagate the --disable-background-timer-throttling flag to the renderer

This flag needs to be passed to the renderer to actually disable
background throttling.

BUG=678745

Review-Url: https://codereview.chromium.org/2624153002
Cr-Commit-Position: refs/heads/master@{#442964}

content/browser/renderer_host/render_process_host_impl.cc

@@ -1669,6 +1669,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kDisable3DAPIs,
     switches::kDisableAcceleratedJpegDecoding,
     switches::kDisableAcceleratedVideoDecode,
+    switches::kDisableBackgroundTimerThrottling,
     switches::kDisableBlinkFeatures,
     switches::kDisableBreakpad,
     switches::kDisablePreferCompositingToLCDText,