Refactor Histogram relationship diagnostics.

tracing/tracing/value/histogram_set_hierarchy.html

Index: tracing/tracing/value/histogram_set_hierarchy.html
diff --git a/tracing/tracing/value/histogram_set_hierarchy.html b/tracing/tracing/value/histogram_set_hierarchy.html
index da23ef4f8708a2f38f15a13f852546ea34416ea0..7caf84934ceeff1bbb99651ff9eee9341b5bdc14 100644
--- a/tracing/tracing/value/histogram_set_hierarchy.html
+++ b/tracing/tracing/value/histogram_set_hierarchy.html
@@ -10,18 +10,6 @@ found in the LICENSE file.
 <script>
 'use strict';
 tr.exportTo('tr.v', function() {
-  function deleteMergedToDiagnostics(histogramArrayMap) {
-    for (const [name, histograms] of histogramArrayMap) {
-      if (histograms instanceof Array) {
-        for (const histogram of histograms) {
-          histogram.diagnostics.delete(tr.v.d.RESERVED_NAMES.MERGED_TO);
-        }
-      } else if (histograms instanceof Map) {
-        deleteMergedToDiagnostics(histograms);
-      }
-    }
-  }
-
   /*
    * See also HistogramSet.groupHistogramsRecursively().
    * See also tr.v.ui.HistogramSetTableRow.
@@ -69,19 +57,6 @@ tr.exportTo('tr.v', function() {
 
       histograms.deduplicateDiagnostics();
 
-      for (const row of HistogramSetHierarchy.walkAll(rootRows)) {
-        for (const [name, hist] of row.columns) {
-          if (!(hist instanceof tr.v.Histogram)) continue;
-          if (!row.mergeRelationshipsForColumn_.get(name)) continue;
-          hist.diagnostics.mergeRelationships(hist);
-        }
-      }
-
-      // Delete "mergedTo" diagnostics from the original Histograms, or else
-      // they'll accumulate as the user re-groups them, and slow down future
-      // mergeRelationships operations.
-      deleteMergedToDiagnostics(histogramArrayMap);
-
       for (const row of HistogramSetHierarchy.walkAll(rootRows)) {
         row.maybeRebin_();
       }
@@ -154,22 +129,6 @@ tr.exportTo('tr.v', function() {
           continue;
         }
 
-        if (!existing.canAddHistogram(histogram)) {
-          // Remember all of the original unmergeable Histograms so that
-          // filter() can keep the rows that match the given HistogramSet even
-          // if the rows will only be able to display (unmergeable).
-          const unmergeableHistograms = new tr.v.HistogramSet([histogram]);
-          const mergedFrom = existing.diagnostics.get(
-              tr.v.d.RESERVED_NAMES.MERGED_FROM);
-          if (mergedFrom !== undefined) {
-            for (const [unusedName, origHist] of mergedFrom) {
-              unmergeableHistograms.addHistogram(origHist);
-            }
-          }
-          row.columns.set(columnName, unmergeableHistograms);
-          continue;
-        }
-
         if (existing.name !== histogram.name) {
           // It won't make sense to merge relationships for this merged
           // Histogram.
@@ -211,64 +170,36 @@ tr.exportTo('tr.v', function() {
     }
 
     /**
-     * Clones and filters |rows| to contain only |histograms|.
+     * Clones and filters |rows| to contain only |histogramNames|.
      *
      * @param {!Array.<HistogramSetHierarchy>} rows
-     * @param {!tr.v.HistogramSet} histograms
+     * @param {!Set.<string>} histogramNames
      * @returns {!Array.<HistogramSetHierarchy>}
      */
-    static filter(rows, histograms) {
+    static filter(rows, histogramNames) {
       const results = [];
       for (const row of rows) {
         let filteredSubRows = [];
         if (row.subRows.length > 0) {
           // This is a branch row. Drop it if all of its subrows were dropped.
           filteredSubRows = HistogramSetHierarchy.filter(
-              row.subRows, histograms);
+              row.subRows, histogramNames);
           if (filteredSubRows.length === 0) continue;
         } else {
           // This is a leaf row. Drop it if none of the Histograms in
-          // |row.columns| were merged from any in |histograms|.
+          // |row.columns| are named in |histogramNames|.
           let found = false;
           for (const testHist of row.columns.values()) {
-            if (testHist instanceof tr.v.HistogramSet) {
-              // Keep this unmergeable cell if it was merged from any of
-              // |histograms|.
-              for (const origHist of testHist) {
-                if (histograms.lookupHistogram(origHist.guid) !== undefined) {
-                  found = true;
-                  break;
-                }
-              }
-              if (found) break;
-
-              continue;
-            }
-
             if (!(testHist instanceof tr.v.Histogram)) {
               throw new Error(
                   'Cells can only contain Histogram or HistogramSet');
             }
 
-            if (histograms.lookupHistogram(testHist.guid) !== undefined) {
+            if (histogramNames.has(testHist.name)) {
               found = true;
               break;
             }
-
-            const mergedFrom = testHist.diagnostics.get(
-                tr.v.d.RESERVED_NAMES.MERGED_FROM);
-            if (mergedFrom !== undefined) {
-              for (const [unusedName, origHist] of mergedFrom) {
-                if (histograms.lookupHistogram(origHist.guid) !== undefined) {
-                  found = true;
-                  break;
-                }
-              }
-            }
-            if (found) break;
           }
-          // If none of the Histograms in |row| were merged from any of
-          // |histograms|, then drop this row.
           if (!found) continue;
         }