Fix deadlock during WebView initialization.

We cannot hold onto a lock that could potentially block the UI thread,
while calling into any getter in WebViewChromiumAwInit related to
chromium initialization. This is because those getters
1. hold a lock,
2. post a chromium-initialization task to the UI thread, and then
3. wait for the task to finish after releasing the lock in 1
So if thread X holds another lock, and calls a WebViewChromiumAwInit
getter, a deadlock occurs if the UI thread tries to hold onto that other
lock before running the chromium-initialization task.

We fix this issue by providing a getLock() method on
WebViewChromiumAwInit for WebViewChromiumFactoryProvider to re-use the
existing lock to guard its member variables (instead of using another
lock).

Bug: 812203
Change-Id: I2e8d69f2667bce1e4312cc821fc804d44b6deaba
Reviewed-on: https://chromium-review.googlesource.com/922823
Commit-Queue: Gustav Sennton <gsennton@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537298}

android_webview/glue/java/src/com/android/webview/chromium/WebViewChromiumAwInit.java

@@ -264,6 +264,15 @@ class WebViewChromiumAwInit {
         return mBrowserContext;
     }
 
+    /**
+     * Returns the lock used for guarding chromium initialization.
+     * We make this package-public to let higher-level classes use this lock to guard variables
+     * dependent on this class, to avoid introducing new locks (which can cause deadlocks).
+     */
+    Object getLock() {
+        return mLock;
+    }
+
     public SharedStatics getStatics() {
         synchronized (mLock) {
             if (mSharedStatics == null) {

android_webview/glue/java/src/com/android/webview/chromium/WebViewChromiumFactoryProvider.java

@@ -115,9 +115,10 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
 
     boolean mShouldDisableThreadChecking;
 
-    // Initialization guarded by mAdapterLock
+    // Initialization guarded by mAwInit.getLock()
     private Statics mStaticsAdapter;
 
+    // TODO(gsennton) remove this when downstream doesn't depend on it anymore
     // Guards accees to adapters.
     // This member is not private only because the downstream subclass needs to access it,
     // it shouldn't be accessed from anywhere else.
@@ -315,9 +316,9 @@ public class WebViewChromiumFactoryProvider implements WebViewFactoryProvider {
 
     @Override
     public Statics getStatics() {
-        synchronized (mAdapterLock) {
+        synchronized (mAwInit.getLock()) {
+            SharedStatics sharedStatics = mAwInit.getStatics();
             if (mStaticsAdapter == null) {
-                SharedStatics sharedStatics = mAwInit.getStatics();
                 mStaticsAdapter = new WebViewChromiumFactoryProvider.Statics() {
                     @Override
                     public String findAddress(String addr) {