[dart] Explicitly convert property to integer

With the new engine (which we do not yet run on the builders), this
property seems to be returned as a floating-point number. This behavior
shows when doing a led run with '-modernize'.

Change-Id: I3dbbcb671fcd81180d27d3dfda8afa4fddfd4342
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/158440
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Karl Klose <karlklose@google.com>
diff --git a/README.recipes.md b/README.recipes.md
index fd7d199..a283e47 100644
--- a/README.recipes.md
+++ b/README.recipes.md
@@ -66,13 +66,13 @@
 
 Deletes the debug log file
 
-&mdash; **def [download\_browser](/recipe_modules/dart/api.py#973)(self, runtime, version):**
+&mdash; **def [download\_browser](/recipe_modules/dart/api.py#975)(self, runtime, version):**
 
 &mdash; **def [get\_secret](/recipe_modules/dart/api.py#74)(self, name):**
 
 Decrypts the specified secret and returns the location of the result
 
-&mdash; **def [has\_infra\_failure](/recipe_modules/dart/api.py#1270)(self, failure):**
+&mdash; **def [has\_infra\_failure](/recipe_modules/dart/api.py#1272)(self, failure):**
 
 Returns whether failure is an aggregated failure that directly or
 indirectly contains an InfraFailure.
diff --git a/recipe_modules/dart/api.py b/recipe_modules/dart/api.py
index 138ab32..94f194c 100644
--- a/recipe_modules/dart/api.py
+++ b/recipe_modules/dart/api.py
@@ -931,7 +931,9 @@
       with self.m.context(cwd=self.m.path['checkout']):
         with self.m.step.nest('download previous results'):
           if self._is_bisecting():
-            latest = self.m.bisect_build.get_base_build()
+            # With the new bbagent infrastructure, this value is returned
+            # as a floating-point value, not an int.
+            latest = int(self.m.bisect_build.get_base_build())
           else:
             latest, _ = self._get_latest_tested_commit()
           self._download_results(latest)