Bug 610852 Check xRGB format for XShm Image r=karlt a=benjamin

widget/src/shared/nsShmImage.cpp

@@ -110,11 +110,19 @@ nsShmImage::Create(const gfxIntSize& aSize,
     shm->mSize = aSize;
     switch (shm->mImage->depth) {
     case 24:
-        shm->mFormat = gfxASurface::ImageFormatRGB24; break;
+        // Only xRGB is supported.
+        if ((shm->mImage->red_mask == 0xff0000) &&
+            (shm->mImage->green_mask == 0xff00) &&
+            (shm->mImage->blue_mask == 0xff)) {
+            shm->mFormat = gfxASurface::ImageFormatRGB24;
+            break;
+        }
+        goto unsupported;
     case 16:
         shm->mFormat = gfxASurface::ImageFormatRGB16_565; break;
+    unsupported:
     default:
-        NS_WARNING("Unsupported XShm Image depth!");
+        NS_WARNING("Unsupported XShm Image format!");
         gShmAvailable = PR_FALSE;
         return nsnull;
     }