Enable precompiled headers for Blink on Windows.

third_party/WebKit/Source/modules/webgl/BUILD.gn

Index: third_party/WebKit/Source/modules/webgl/BUILD.gn
diff --git a/third_party/WebKit/Source/modules/webgl/BUILD.gn b/third_party/WebKit/Source/modules/webgl/BUILD.gn
index 285f3968307b379acc2f48809c85ee96970ba7c3..85b7b325f8830043c07c53e4ae35020fe8c63915 100644
--- a/third_party/WebKit/Source/modules/webgl/BUILD.gn
+++ b/third_party/WebKit/Source/modules/webgl/BUILD.gn
@@ -123,4 +123,9 @@ blink_modules_sources("webgl") {
     "WebGLVertexArrayObjectOES.cpp",
     "WebGLVertexArrayObjectOES.h",
   ]
+
+  # The modules/webgl/ directly is a larger module, and
+  # the implementation depends on a fair chunk of core/ --
+  # include the core pch for faster Windows compilation times.
+  configs += [ "//third_party/WebKit/Source/core:blink_core_pch" ]
 }