Add an error check to ANGLE DLL update script.

scripts/update_canary_angle.py

@@ -25,6 +25,8 @@ source_paths = [
     os.path.join('..', 'out', 'Release_x64'),
 ]
 
+script_dir = os.path.dirname(sys.argv[0])
+
 # Default Canary installation path.
 chrome_folder = os.path.join(os.environ['LOCALAPPDATA'], 'Google', 'Chrome SxS', 'Application')
 
@@ -33,13 +35,16 @@ binary_name = 'libGLESv2.dll'
 newest_folder = None
 newest_mtime = None
 for path in source_paths:
-    binary_path = os.path.join(path, binary_name)
+    binary_path = os.path.join(script_dir, path, binary_name)
     if os.path.exists(binary_path):
         binary_mtime = os.path.getmtime(binary_path)
         if (newest_folder is None) or (binary_mtime > newest_mtime):
-            newest_folder = path
+            newest_folder = os.path.join(script_dir, path)
             newest_mtime = binary_mtime
 
+if newest_folder is None:
+    sys.exit("Could not find ANGLE DLLs!")
+
 source_folder = newest_folder
 
 # Is a folder a chrome binary directory?