[Cronet] Add ExperimentalCronetEngine.Builder.setThreadPriority() API

components/cronet/android/java/src/org/chromium/net/impl/CronetEngineBuilderImpl.java

Index: components/cronet/android/java/src/org/chromium/net/impl/CronetEngineBuilderImpl.java
diff --git a/components/cronet/android/java/src/org/chromium/net/impl/CronetEngineBuilderImpl.java b/components/cronet/android/java/src/org/chromium/net/impl/CronetEngineBuilderImpl.java
index 813db69beacbecebce23fa9b37d66141ef557c83..02d2555ec3c1f995a1677b2abacc1517d5bc495b 100644
--- a/components/cronet/android/java/src/org/chromium/net/impl/CronetEngineBuilderImpl.java
+++ b/components/cronet/android/java/src/org/chromium/net/impl/CronetEngineBuilderImpl.java
@@ -3,6 +3,8 @@
 // found in the LICENSE file.
 package org.chromium.net.impl;
 
+import static android.os.Process.THREAD_PRIORITY_LOWEST;
+
 import android.content.Context;
 import android.support.annotation.IntDef;
 import android.support.annotation.VisibleForTesting;
@@ -71,6 +73,8 @@ public abstract class CronetEngineBuilderImpl extends ICronetEngineBuilder {
 
     private static final Pattern INVALID_PKP_HOST_NAME = Pattern.compile("^[0-9\\.]*$");
 
+    private static final int INVALID_THREAD_PRIORITY = THREAD_PRIORITY_LOWEST + 1;
+
     // Private fields are simply storage of configuration for the resulting CronetEngine.
     // See setters below for verbose descriptions.
     private final Context mApplicationContext;
@@ -91,6 +95,7 @@ public abstract class CronetEngineBuilderImpl extends ICronetEngineBuilder {
     protected long mMockCertVerifier;
     private boolean mNetworkQualityEstimatorEnabled;
     private String mCertVerifierData;
+    private int mThreadPriority = INVALID_THREAD_PRIORITY;
 
     /**
      * Default config enables SPDY, disables QUIC, SDCH and HTTP cache.
@@ -387,6 +392,22 @@ public abstract class CronetEngineBuilderImpl extends ICronetEngineBuilder {
         return mCertVerifierData;
     }
 
+    @Override
+    public CronetEngineBuilderImpl setThreadPriority(int priority) {
+        if (priority > THREAD_PRIORITY_LOWEST || priority < -20) {
+            throw new IllegalArgumentException("Thread priority invalid");
+        }
+        mThreadPriority = priority;
+        return this;
+    }
+
+    /**
+     * @returns thread priority provided by user, or {@code defaultThreadPriority} if none provided.
+     */
+    int threadPriority(int defaultThreadPriority) {
+        return mThreadPriority == INVALID_THREAD_PRIORITY ? defaultThreadPriority : mThreadPriority;

[mef, 2017/05/15 17:20:11]

can we just default |mThreadPriority| to sensible defaultThreadPriority?

[pauljensen, 2017/05/15 19:03:25]

I feel that could have significant impact on performance.  I think we should
have an embedder experiment with the background+1 priority, and if that looks
good, then use it for the default.

[mef, 2017/05/16 15:51:29]

Sounds good, it makes sense to experiment.

+    }
+
     /**
      * Returns {@link Context} for builder.
      *