Normalize thread_times metric against the bounds of the browser process.

tracing/tracing/model/helpers/chrome_model_helper.html

Index: tracing/tracing/model/helpers/chrome_model_helper.html
diff --git a/tracing/tracing/model/helpers/chrome_model_helper.html b/tracing/tracing/model/helpers/chrome_model_helper.html
index 5aee6578dfc475b1e51f57ad88622de0d94ce6f7..43444a23f1f831e799d934a2a18e37b9338a3518 100644
--- a/tracing/tracing/model/helpers/chrome_model_helper.html
+++ b/tracing/tracing/model/helpers/chrome_model_helper.html
@@ -138,6 +138,29 @@ tr.exportTo('tr.model.helpers', function() {
       if (largestPid === -1) return undefined;
 
       return this.rendererHelpers[largestPid];
+    },
+
+    // Returns the minimal bounds that includes all Chrome-related slices. This
+    // relies on the assumption that all Chrome-relevant traces are bounded by
+    // the browser process. Returns null if the minimal bounds could not be
+    // established.
+    get chromeBounds() {
+      if (!this.cachedChromeBounds_) {
+        var bounds = new tr.b.Range();
+
+        function updateBounds(process) {
+          for (var tid in process.threads) {
+            bounds.addRange(process.threads[tid].bounds);
+          }
+        }
+        for (var pid in this.browserHelpers) {
+          updateBounds(this.browserHelpers[pid].process);
+        }
+        this.cachedChromeBounds_ = bounds;
+      }
+      if (this.cachedChromeBounds_.isEmpty)
+        return null;
+      return this.cachedChromeBounds_;
     }
   };