[test] Rework how default timeout is handled.

The slow_archs list had only an effect when no timeout was
passed. Now it will also increase the timeout on the bots.

Also simplified the code a bit.

Review URL: https://codereview.chromium.org/1866953002

Cr-Commit-Position: refs/heads/master@{#35355}

tools/run-tests.py

@@ -337,7 +337,7 @@ def BuildOptions():
   result.add_option("--time", help="Print timing information after running",
                     default=False, action="store_true")
   result.add_option("-t", "--timeout", help="Timeout in seconds",
-                    default= -1, type="int")
+                    default=TIMEOUT_DEFAULT, type="int")
   result.add_option("--tsan",
                     help="Regard test expectations for TSAN",
                     default=False, action="store_true")
@@ -665,19 +665,16 @@ def Execute(arch, mode, args, options, suites):
 
   # Populate context object.
   mode_flags = MODES[mode]["flags"]
-  timeout = options.timeout
-  if timeout == -1:
-    # Simulators are slow, therefore allow a longer default timeout.
+
+  # Simulators are slow, therefore allow a longer timeout.
   if arch in SLOW_ARCHS:
-      timeout = 2 * TIMEOUT_DEFAULT;
-    else:
-      timeout = TIMEOUT_DEFAULT;
+    options.timeout *= 2
 
-  timeout *= MODES[mode]["timeout_scalefactor"]
+  options.timeout *= MODES[mode]["timeout_scalefactor"]
 
   if options.predictable:
     # Predictable mode is slower.
-    timeout *= 2
+    options.timeout *= 2
 
   # TODO(machenbach): Remove temporary verbose output on windows after
   # debugging driver-hung-up on XP.
@@ -687,7 +684,8 @@ def Execute(arch, mode, args, options, suites):
   )
   ctx = context.Context(arch, MODES[mode]["execution_mode"], shell_dir,
                         mode_flags, verbose_output,
-                        timeout, options.isolates,
+                        options.timeout,
+                        options.isolates,
                         options.command_prefix,
                         options.extra_flags,
                         options.no_i18n,