Copied from: https://hg.mozilla.org/releases/mozilla-esr38/rev/94a95291d095
Security advisory: https://www.mozilla.org/en-US/security/advisories/mfsa2016-01/
Mozilla Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1224200

# HG changeset patch
# User Timothy Nikkel <tnikkel@gmail.com>
# Date 1453303652 -3600
# Node ID 94a95291d0958439dbed5b7dc99fae59e1318592
# Parent  999c13acb40e1113306c65925a7d96688339d945
Bug 1224200 - Allow downscaler to get (and ignore) new input lines after it has finished producing all output lines. r=seth, a=lizzard

diff --git a/image/src/Downscaler.cpp b/image/src/Downscaler.cpp
--- a/image/src/Downscaler.cpp
+++ b/image/src/Downscaler.cpp
@@ -145,43 +145,44 @@ GetFilterOffsetAndLength(UniquePtr<skia:
                           aFilterLengthOut);
 }
 
 void
 Downscaler::CommitRow()
 {
   MOZ_ASSERT(mOutputBuffer, "Should have a current frame");
   MOZ_ASSERT(mCurrentInLine < mOriginalSize.height, "Past end of input");
-  MOZ_ASSERT(mCurrentOutLine < mTargetSize.height, "Past end of output");
 
-  int32_t filterOffset = 0;
-  int32_t filterLength = 0;
-  GetFilterOffsetAndLength(mYFilter, mCurrentOutLine,
-                           &filterOffset, &filterLength);
+  if (mCurrentOutLine < mTargetSize.height) {
+    int32_t filterOffset = 0;
+    int32_t filterLength = 0;
+    GetFilterOffsetAndLength(mYFilter, mCurrentOutLine,
+                             &filterOffset, &filterLength);
 
-  int32_t inLineToRead = filterOffset + mLinesInBuffer;
-  MOZ_ASSERT(mCurrentInLine <= inLineToRead, "Reading past end of input");
-  if (mCurrentInLine == inLineToRead) {
-    skia::ConvolveHorizontally(mRowBuffer.get(), *mXFilter,
-                               mWindow[mLinesInBuffer++], mHasAlpha,
-                               /* use_sse2 = */ true);
-  }
-
-  MOZ_ASSERT(mCurrentOutLine < mTargetSize.height,
-             "Writing past end of output");
-
-  while (mLinesInBuffer == filterLength) {
-    DownscaleInputLine();
-
-    if (mCurrentOutLine == mTargetSize.height) {
-      break;  // We're done.
+    int32_t inLineToRead = filterOffset + mLinesInBuffer;
+    MOZ_ASSERT(mCurrentInLine <= inLineToRead, "Reading past end of input");
+    if (mCurrentInLine == inLineToRead) {
+      skia::ConvolveHorizontally(mRowBuffer.get(), *mXFilter,
+                                 mWindow[mLinesInBuffer++], mHasAlpha,
+                                 /* use_sse2 = */ true);
     }
 
-    GetFilterOffsetAndLength(mYFilter, mCurrentOutLine,
-                             &filterOffset, &filterLength);
+    MOZ_ASSERT(mCurrentOutLine < mTargetSize.height,
+               "Writing past end of output");
+
+    while (mLinesInBuffer == filterLength) {
+      DownscaleInputLine();
+
+      if (mCurrentOutLine == mTargetSize.height) {
+        break;  // We're done.
+      }
+
+      GetFilterOffsetAndLength(mYFilter, mCurrentOutLine,
+                               &filterOffset, &filterLength);
+    }
   }
 
   mCurrentInLine += 1;
 }
 
 bool
 Downscaler::HasInvalidation() const
 {