Bug 1516033. Make CONTENT_FRAME_TIME_REASON use the same timing as CONTENT_FRAME_TIME. r=mattwoodrow

It perhaps makes more sense to use the start of refresh but I'd like to switch
to the start of the paint so that we get more consistent results between the
two probes.

Differential Revision: https://phabricator.services.mozilla.com/D15236

--HG--
extra : moz-landing-system : lando

gfx/layers/ipc/LayerTransactionParent.cpp

@@ -905,9 +905,6 @@ TransactionId LayerTransactionParent::FlushTransactionId(
     // frame increases. This is effectively including the RecvUpdate work as
     // part of the 'compositing' phase for this metric, but it isn't included in
     // COMPOSITE_TIME, and *is* included in CONTENT_FULL_PAINT_TIME.
-    latencyMs = (aCompositeEnd - mRefreshStartTime).ToMilliseconds();
-    latencyNorm = latencyMs / mVsyncRate.ToMilliseconds();
-    fracLatencyNorm = lround(latencyNorm * 100.0);
     if (fracLatencyNorm < 200) {
       // Success
       Telemetry::AccumulateCategorical(

gfx/layers/wr/WebRenderBridgeParent.cpp

@@ -1976,10 +1976,6 @@ TransactionId WebRenderBridgeParent::FlushTransactionIdsForEpoch(
 
       // Record CONTENT_FRAME_TIME_REASON.
       //
-      // This uses the refresh start time (CONTENT_FRAME_TIME uses the start of
-      // display list building), since that includes layout/style time, and 200
-      // should correlate more closely with missing a vsync.
-      //
       // Also of note is that when the root WebRenderBridgeParent decides to
       // skip a composite (due to the Renderer being busy), that won't notify
       // child WebRenderBridgeParents. That failure will show up as the
@@ -1992,9 +1988,6 @@ TransactionId WebRenderBridgeParent::FlushTransactionIdsForEpoch(
       // child pipelines contained within a render, after it finishes, but I
       // can't see how to query what child pipeline would have been rendered,
       // when we choose to not do it.
-      latencyMs = (aEndTime - transactionId.mRefreshStartTime).ToMilliseconds();
-      latencyNorm = latencyMs / mVsyncRate.ToMilliseconds();
-      fracLatencyNorm = lround(latencyNorm * 100.0);
       if (fracLatencyNorm < 200) {
         // Success
         Telemetry::AccumulateCategorical(