Move some calls from the Android UI thread to the Chrome one

android_webview/java/src/org/chromium/android_webview/AwContents.java

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index ebebc65756f431bc1ee8074423dde2d1b2e5ccef..1bcf5fa42694aa6c6535199b168bdc2725503043 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -640,7 +640,12 @@ public void onTrimMemory(final int level) {
             if (isDestroyed(NO_WARN)) return;
             boolean visibleRectEmpty = getGlobalVisibleRect().isEmpty();
             final boolean visible = mIsViewVisible && mIsWindowVisible && !visibleRectEmpty;
-            nativeTrimMemory(mNativeAwContents, level, visible);
+            ThreadUtils.runOnUiThread(new Runnable() {

[boliu, 2015/12/10 22:03:14]

I think new code is not wrong, but I kinda want to revert back to old code here:

Webview relies the the trim call to be delivered synchronously. That's why it's
not using MemoryPressureListener here. So new code is not broken since
runOnuiThread is also synchronous if this is the UI thread. But assuming
runOnuiThread behavior is bad imo.

So there are a few cases:
1) all webviews used on a single non-main thread, has activity context, then the
whole activity lives on that thread, and all the trim signals also gets
delivered on that thread, so both new and old code are fine
2) all webview used on a single non-main thread, has global application context,
then I guess new code is more correct then old code, but then every access to
app context is not thread safe already, and this is only one of them, so
probably not worth worrying too much (app context affects case 1 too, but let's
not think too hard on that..)
3) webviews used from multiple threads, and then gets merged to a single
chromium UI thread (context doesn't matter), I don't ever see this scenario
being thread safe, since chromium will be access all the view tree on its UI
thread, so again not worth worrying about this case imo

Maybe we should test 1) and crash hard on 2) and 3)?

Other webview owners have thoughts here?

+                @Override
+                public void run() {
+                    nativeTrimMemory(mNativeAwContents, level, visible);
+                }
+            });
         }
 
         @Override