CustomTabs: Base version for prerender switch

chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java

Index: chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
index 4c3eee8e7a1e3ffcf42febc2b7ac428fd24caedf..da7d69700fa42a9cf0f4bee91abd9f3b1815d6b4 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
@@ -89,6 +89,11 @@ public class CustomTabsConnection {
     @VisibleForTesting
     static final int PREFETCH_ONLY = 2;
 
+    @VisibleForTesting
+    static final String PRERENDER_MODE_KEY = "android.support.customtabs.PRERENDER_MODE";
+    @VisibleForTesting
+    static final int DEFAULT_PRERENDER = 0;

[ahemery, 2017/03/16 17:28:35]

Not sure of the name

+
     private static AtomicReference<CustomTabsConnection> sInstance = new AtomicReference<>();
 
     /** Holds the parameters for the current speculation. */
@@ -126,6 +131,8 @@ public class CustomTabsConnection {
 
     @VisibleForTesting
     SpeculationParams mSpeculation;
+    @VisibleForTesting
+    int mPrerenderMode;
     protected final Application mApplication;
     protected final ClientManager mClientManager;
     private final boolean mLogRequests;
@@ -333,7 +340,7 @@ public class CustomTabsConnection {
                 didStartPrefetch = new ResourcePrefetchPredictor(profile).startPrefetching(url);
                 if (didStartPrefetch) mSpeculation = SpeculationParams.forPrefetch(session, url);
             } else if (debugOverrideValue != NO_PRERENDERING) {
-                didStartPrerender = prerenderUrl(session, url, extras, uid);
+                didStartPrerender = startPrerender(session, url, extras, uid);
             }
         }
         preconnectUrls(otherLikelyBundles);
@@ -900,8 +907,19 @@ public class CustomTabsConnection {
         return !cm.isActiveNetworkMetered() || shouldPrerenderOnCellularForSession(session);
     }
 
-    /** Cancels a prerender for a given session, or any session if null. */
+    @VisibleForTesting
     void cancelPrerender(CustomTabsSessionToken session) {

[ahemery, 2017/03/16 17:28:35]

Generic function to cancel the prerendering of a URL

+        switch (mPrerenderMode) {
+            case DEFAULT_PRERENDER:
+                cancelWebContentsPrerender(session);
+                break;
+            default:
+                return;
+        }
+    }
+
+    /** Cancels a prerender for a given session, or any session if null. */
+    private void cancelWebContentsPrerender(CustomTabsSessionToken session) {

[ahemery, 2017/03/16 17:28:35]

Version targeting what we know typically as "prerender". Running out of names
here...

         ThreadUtils.assertOnUiThread();
         if (mSpeculation != null && (session == null || session.equals(mSpeculation.session))
                 && mSpeculation.webContents != null) {
@@ -911,6 +929,18 @@ public class CustomTabsConnection {
         }
     }
 
+    private boolean startPrerender(

[ahemery, 2017/03/16 17:28:35]

Generic function to start prerendering a URL

+            CustomTabsSessionToken session, String url, Bundle extras, int uid) {
+        // Last one wins and cancels the previous prerender.
+        cancelPrerender(null);
+        switch (mPrerenderMode) {
+            case DEFAULT_PRERENDER:
+                return prerenderUrl(session, url, extras, uid);
+            default:
+                return false;
+        }
+    }
+
     /**
      * Tries to request a prerender for a given URL.
      *
@@ -923,12 +953,8 @@ public class CustomTabsConnection {
     private boolean prerenderUrl(
             CustomTabsSessionToken session, String url, Bundle extras, int uid) {
         ThreadUtils.assertOnUiThread();
-        // Ignores mayPrerender() for an empty URL, since it cancels an existing prerender.

[ahemery, 2017/03/16 17:28:35]

This is already done in maylaunchUrl and it makes more sense to be done there.
Since the function is private, we are sure no other unexpected callers relying
on this behaviour exist.

-        if (!mayPrerender(session) && !TextUtils.isEmpty(url)) return false;
         if (!mWarmupHasBeenCalled.get()) return false;
-        // Last one wins and cancels the previous prerender.
-        cancelPrerender(null);
-        if (TextUtils.isEmpty(url)) return false;
+
         boolean throttle = !shouldPrerenderOnCellularForSession(session);
         if (throttle && !mClientManager.isPrerenderingAllowed(uid)) return false;
 
@@ -947,18 +973,17 @@ public class CustomTabsConnection {
             referrer = getReferrerForSession(session).getUrl();
         }
         if (referrer == null) referrer = "";
-        Pair<WebContents, WebContents> webContentsPair = mExternalPrerenderHandler.addPrerender(

[ahemery, 2017/03/16 17:28:35]

Auto formatting

-                Profile.getLastUsedProfile(), url, referrer,
-                contentBounds,
-                shouldPrerenderOnCellularForSession(session));
+        Pair<WebContents, WebContents> webContentsPair =
+                mExternalPrerenderHandler.addPrerender(Profile.getLastUsedProfile(), url, referrer,
+                        contentBounds, shouldPrerenderOnCellularForSession(session));
         if (webContentsPair == null) return false;
         WebContents dummyWebContents = webContentsPair.first;
         if (webContentsPair.second != null) {
             mClientManager.resetPostMessageHandlerForSession(session, webContentsPair.second);
         }
         if (throttle) mClientManager.registerPrerenderRequest(uid, url);
-        mSpeculation = SpeculationParams.forPrerender(

[ahemery, 2017/03/16 17:28:35]

Auto formatting

-                session, url, dummyWebContents, referrer, extras);
+        mSpeculation =
+                SpeculationParams.forPrerender(session, url, dummyWebContents, referrer, extras);
 
         RecordHistogram.recordBooleanHistogram("CustomTabs.PrerenderSessionUsesDefaultParameters",
                 mClientManager.usesDefaultSessionParameters(session));
@@ -980,4 +1005,13 @@ public class CustomTabsConnection {
     void setForcePrerender(boolean force) {
         mForcePrerenderForTesting = force;
     }
+
+    @VisibleForTesting
+    void setPrerenderMode(int mode) {

[ahemery, 2017/03/16 17:28:35]

The new switch that enables toggling between usual prerender and other modes
(e.g. hidden tab). The clear is done to avoid mixed states.

+        if (mPrerenderMode != mode) {
+            // Remove all existing speculations when switching mode
+            cancelPrerender(null);
+            mPrerenderMode = mode;
+        }
+    }
 }