Workaround qualcomm-specific activity restore bug

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 d24cb7cbeccd81287981368ba41df25e6c645c9f..9060c091319daeb93e497aee886b4e3450569c6e 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -278,6 +278,10 @@ public class AwContents implements SmartClipProvider,
     // through the resourcethrottle. This is only used for popup windows.
     private boolean mDeferredShouldOverrideUrlLoadingIsPendingForPopup;
 
+    // This is a workaround for some qualcomm devices discarding buffer on
+    // Activity restore.
+    private boolean mInvalidateRootViewOnNextDraw;
+
     // The framework may temporarily detach our container view, for example during layout if
     // we are a child of a ListView. This may cause many toggles of View focus, which we suppress
     // when in this state.
@@ -2213,6 +2217,8 @@ public class AwContents implements SmartClipProvider,
     }
 
     private void setWindowVisibilityInternal(boolean visible) {
+        mInvalidateRootViewOnNextDraw |= Build.VERSION.SDK_INT <= Build.VERSION_CODES.LOLLIPOP
+                && visible && !mIsWindowVisible;
         mIsWindowVisible = visible;
         if (!isDestroyed()) nativeSetWindowVisibility(mNativeAwContents, mIsWindowVisible);
     }
@@ -2732,6 +2738,11 @@ public class AwContents implements SmartClipProvider,
                     mScrollOffsetManager.computeMaximumVerticalScrollOffset())) {
                 postInvalidateOnAnimation();
             }
+
+            if (mInvalidateRootViewOnNextDraw) {
+                mContainerView.getRootView().invalidate();
+                mInvalidateRootViewOnNextDraw = false;
+            }
         }
 
         @Override