Proof of concept for running extension API stack through dev tools.

tools/telemetry/telemetry/desktop_browser_backend.py

Index: tools/telemetry/telemetry/desktop_browser_backend.py
diff --git a/tools/telemetry/telemetry/desktop_browser_backend.py b/tools/telemetry/telemetry/desktop_browser_backend.py
index 43ac0b5c1588aa830486a146afd33c6a873e14d1..9797e7bad15e764bfc64bf14c4e362870849e2b8 100644
--- a/tools/telemetry/telemetry/desktop_browser_backend.py
+++ b/tools/telemetry/telemetry/desktop_browser_backend.py
@@ -27,6 +27,9 @@ class DesktopBrowserBackend(browser_backend.BrowserBackend):
     if not self._executable:
       raise Exception('Cannot create browser, no executable found!')
 
+    if len(options.extensions_to_load) > 0 and is_content_shell:
+      raise Exception('Cannot load extensions for content shell!')
+
     self._port = DEFAULT_PORT
     args = [self._executable]
     args.extend(self.GetBrowserStartupArgs())
@@ -52,6 +55,17 @@ class DesktopBrowserBackend(browser_backend.BrowserBackend):
     if not self.options.dont_override_profile:
       self._tmpdir = tempfile.mkdtemp()
       args.append('--user-data-dir=%s' % self._tmpdir)
+    extensions = ','.join(
+        [extension.path for extension in self.options.extensions_to_load
+         if not extension.is_component])
+    component_extensions = ','.join(
+        [extension.path for extension in self.options.extensions_to_load
+         if extension.is_component])
+    if len(extensions) > 0:
+      args.append('--load-extension=%s' % extensions)
+    if len(component_extensions) > 0:
+      args.append('--load-component-extension=%s' % component_extensions)
+
     return args
 
   def IsBrowserRunning(self):