Fix correctness issues in timing

Author: gregtatum

src/profile-logic/merge-compare.js

@@ -218,17 +218,14 @@ export function mergeProfilesForDiffing(
     // We adjust the various times so that the 2 profiles are aligned at the
     // start and the data is consistent.
     let startTimeAdjustment = 0;
-    if (thread.samples.length !== 0) {
+    if (thread.samples.length) {
       startTimeAdjustment = -thread.samples.time[0];
-    }
-    if (thread.markers.length !== 0) {
+    } else if (thread.markers.length) {
       for (const startTime of thread.markers.startTime) {
+        // Find the first marker startTime.
         if (startTime !== null) {
-          if (startTimeAdjustment === 0) {
-            startTimeAdjustment = startTime;
-          } else {
-            startTimeAdjustment = Math.min(startTime, startTimeAdjustment);
-          }
+          startTimeAdjustment = -startTime;
+          break;
         }
       }
     }

src/test/store/actions.test.js

@@ -518,8 +518,8 @@ describe('selectors/getThreadRange', function () {
     );
 
     expect(selectedThreadSelectors.getThreadRange(getState())).toEqual({
-      start: 10,
-      end: 21,
+      start: 0,
+      end: 11,
     });
   });
 

src/test/unit/merge-compare.test.js

@@ -261,8 +261,8 @@ describe('mergeProfilesForDiffing function', function () {
     ]);
 
     expect(getTimeRangeIncludingAllThreads(profile)).toEqual({
-      end: 21,
-      start: 4,
+      start: 0,
+      end: 11,
     });
   });
 });