Android: Start up GPU channel early

This addresses a TODO and reverts
https://codereview.chromium.org/777303004.

With https://codereview.chromium.org/889083002
the CrashDumpManager is now initialized earlier so
things should be fine.

BUG=439322

Review URL: https://codereview.chromium.org/893393004

Cr-Commit-Position: refs/heads/master@{#315170}

content/browser/browser_main_loop.cc

@@ -1077,8 +1077,7 @@ int BrowserMainLoop::BrowserThreadsStarted() {
   }
 #endif
 #elif defined(OS_ANDROID)
-  // TODO(crbug.com/439322): This should be set to |true|.
-  established_gpu_channel = false;
+  established_gpu_channel = true;
   BrowserGpuChannelHostFactory::Initialize(established_gpu_channel);
 #endif