content: Improve thread priority for raster threads.

base/threading/platform_thread_android.cc

Index: base/threading/platform_thread_android.cc
diff --git a/base/threading/platform_thread_android.cc b/base/threading/platform_thread_android.cc
index 1e4ae93fcf29c657af2362b2fcae75011f539a33..e6a5ef5bd44a81ea21d9aab06366d70399197f5d 100644
--- a/base/threading/platform_thread_android.cc
+++ b/base/threading/platform_thread_android.cc
@@ -24,15 +24,13 @@ namespace base {
 
 namespace internal {
 
-// - BACKGROUND is 9 due to it being the nicest value we can use that's still
-// above an Android system threshold that enables heavy throttling starting at
-// 10; we want to be lower-priority than Chrome's other threads without
-// incurring this behavior.
+// - BACKGROUND corresponds to Android's PRIORITY_BACKGROUND = 10 value and can

[aelias_OOO_until_Jul13, 2016/02/23 23:01:40]

Could you write in the comment here that this priority will force the thread
onto a little core in big.LITTLE CPUs?  (I couldn't say so when I wrote the
previous comment because Android-team wanted to keep the existence of big.LITTLE
Nexus devices secret, but it's public knowledge now.)

[reveman, 2016/02/24 17:08:54]

Done.

+// result in heavy throttling.
 // - DISPLAY is -6 due to being midway between Android's DISPLAY (-4) and
 // URGENT_DISPLAY (-8).
-// - REALTIME_AUDIO corresponds to Android's THREAD_PRIORITY_AUDIO = -16 value.
+// - REALTIME_AUDIO corresponds to Android's PRIORITY_AUDIO = -16 value.
 const ThreadPriorityToNiceValuePair kThreadPriorityToNiceValueMap[4] = {
-    {ThreadPriority::BACKGROUND, 9},
+    {ThreadPriority::BACKGROUND, 10},
     {ThreadPriority::NORMAL, 0},
     {ThreadPriority::DISPLAY, -6},
     {ThreadPriority::REALTIME_AUDIO, -16},