[Telemetry] Default to most recent local build if --browser is omitted.

tools/telemetry/telemetry/page/page_runner.py

Index: tools/telemetry/telemetry/page/page_runner.py
diff --git a/tools/telemetry/telemetry/page/page_runner.py b/tools/telemetry/telemetry/page/page_runner.py
index 8e20cec1ca85975a9e8be541e80b1ecb70fb2d90..ce849823eff87ba41d49962ea6117fcb6ebf5be6 100644
--- a/tools/telemetry/telemetry/page/page_runner.py
+++ b/tools/telemetry/telemetry/page/page_runner.py
@@ -154,10 +154,16 @@ def Run(test, page_set, expectations, options):
 
   # Create a possible_browser with the given options.
   test.CustomizeBrowserOptions(options)
-  possible_browser = browser_finder.FindBrowser(options)
+  try:
+    possible_browser = browser_finder.FindBrowser(options)
+  except browser_finder.BrowserTypeRequiredException, e:
+    sys.stderr.write(str(e) + '\n')
+    sys.exit(1)
   if not possible_browser:
-    raise Exception('No browser found.\n'
-        'Use --browser=list to figure out which are available.')
+    sys.stderr.write(
+        'No browser found. Available browsers:\n' +
+        '\n'.join(browser_finder.GetAllAvailableBrowserTypes(options)) + '\n')
+    sys.exit(1)
 
   # Reorder page set based on options.
   pages = _ShuffleAndFilterPageSet(page_set, options)