Use high performance GPU by default in GPU tests.

Upcoming CLs will change the heuristics for selecting the low-power
vs. high-performance GPUs on dual-GPU systems, macOS in particular.
The GPU tests in Chromium's hardware fleet expect to run on the
high-power GPU, so maintain this behavior by default.

Bug: 965842
Change-Id: I17707475a4505905ea95a8a57d06a1754fc101fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1665910Reviewed-by: ccameron <ccameron@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670302}

content/test/gpu/gpu_tests/gpu_integration_test.py

@@ -86,6 +86,13 @@ class GpuIntegrationTest(
     browser_args.append(
       '--disable-gpu-process-for-dx12-vulkan-info-collection')
 
+    if not ('--force_low_power_gpu' in browser_args or
+            '--force_high_performance_gpu' in browser_args):
+      # Force the GPU tests to use the high-performance GPU on dual-GPU machines
+      # by default. In Chromium's hardware fleet this currently only has an
+      # effect on the dual-GPU MacBook Pros.
+      browser_args.append('--force_high_performance_gpu')
+
     # Append the new arguments.
     browser_options.AppendExtraBrowserArgs(browser_args)
     cls._last_launched_browser_args = set(browser_args)