ui: Sanitize timespan passed to timeline.updateVisibleTime()

- Don't allow the timespan to become shorter than 10ns.
- Use timespan.fitWithin rather than timespan.intersect to avoid
  changing the duration.

Bug: 352566470
Change-Id: I1f85b46f80bb25e58ff0ddeaa72e7ef9a111883f

ui/src/common/high_precision_time_span.ts

@@ -167,6 +167,18 @@ export class HighPrecisionTimeSpan {
     return this;
   }
 
+  /**
+   * Clamp duration to some minimum value. The start remains the same, just the
+   * duration is changed.
+   */
+  clampDuration(minDuration: number): HighPrecisionTimeSpan {
+    if (this.duration < minDuration) {
+      return new HighPrecisionTimeSpan(this.start, minDuration);
+    } else {
+      return this;
+    }
+  }
+
   /**
    * Checks whether this span completely contains a time instant.
    */

ui/src/common/high_precision_time_span_unittest.ts

@@ -122,6 +122,15 @@ describe('HighPrecisionTimeSpan', () => {
     expect(result.duration).toBeCloseTo(1);
   });
 
+  test('clampDuration', () => {
+    const span = new HPTimeSpan(hptime('5'), 1);
+    const clamped = span.clampDuration(10);
+
+    expect(clamped.start.integral).toBe(5n);
+    expect(clamped.start.fractional).toBeCloseTo(0);
+    expect(clamped.duration).toBeCloseTo(10);
+  });
+
   test('equality', () => {
     const span = new HPTimeSpan(hptime('10'), 10);
     expect(span.equals(span)).toBe(true);

ui/src/frontend/timeline.ts

@@ -18,7 +18,6 @@ import {HighPrecisionTimeSpan} from '../common/high_precision_time_span';
 import {Area, State} from '../common/state';
 import {raf} from '../core/raf_scheduler';
 import {Store} from '../public';
-
 import {ratelimit} from './rate_limiters';
 
 interface Range {
@@ -110,10 +109,10 @@ export class Timeline {
 
   // Set visible window using a high precision time span
   updateVisibleTimeHP(ts: HighPrecisionTimeSpan) {
-    this._visibleWindow = ts.intersect(
-      this.traceSpan.start,
-      this.traceSpan.end,
-    );
+    this._visibleWindow = ts
+      .clampDuration(MIN_DURATION)
+      .fitWithin(this.traceSpan.start, this.traceSpan.end);
+
     this.rateLimitedPoker();
   }