Merge 133550 - [Chromium] Unicode combining diacritical aren't always combined on Linux

Source/WebCore/platform/graphics/harfbuzz/ng/HarfBuzzShaper.cpp

Index: Source/WebCore/platform/graphics/harfbuzz/ng/HarfBuzzShaper.cpp
===================================================================
--- Source/WebCore/platform/graphics/harfbuzz/ng/HarfBuzzShaper.cpp	(revision 134170)
+++ Source/WebCore/platform/graphics/harfbuzz/ng/HarfBuzzShaper.cpp	(working copy)
@@ -322,6 +322,11 @@
         HarfBuzzRun* currentRun = m_harfbuzzRuns[runIndex].get();
         const SimpleFontData* currentFontData = currentRun->fontData();
 
+        // Add a space as pre-context to the buffer. This prevents showing dotted-circle
+        // for combining marks at the beginning of runs.
+        static const uint16_t preContext = ' ';
+        hb_buffer_add_utf16(harfbuzzBuffer.get(), &preContext, 1, 1, 0);
+
         if (m_font->isSmallCaps() && u_islower(m_normalizedBuffer[currentRun->startIndex()])) {
             String upperText = String(m_normalizedBuffer.get() + currentRun->startIndex(), currentRun->numCharacters());
             upperText.makeUpper();