Fix keyword of image-rendering and text-align

image-rendering's camel-case keyword does not follow normal
convention because it comes from a different format.
https://developer.mozilla.org/en/docs/Web/CSS/image-rendering#Specifications
text-align's webkit keyword is a webkit prefix keywords, if we can decide
we should follow the convention of CSS property to be consistent.

Bug: 
Change-Id: I0fea055fe67ea521ad0456ef120ba91adf273267
Reviewed-on: https://chromium-review.googlesource.com/566142
Commit-Queue: Minh-Duc Nguyen <nmduc@google.com>
Reviewed-by: Darren Shen <shend@chromium.org>
Reviewed-by: nainar <nainar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485553}

third_party/WebKit/Source/core/css/CSSProperties.json5

@@ -1467,7 +1467,7 @@
       name: "image-rendering",
       inherited: true,
       field_template: "keyword",
-      keywords: ["auto", "optimize-speed", "optimize-quality", "-webkit-optimize-contrast", "pixelated"],
+      keywords: ["auto", "optimizeSpeed", "optimizeQuality", "-webkit-optimize-contrast", "pixelated"],
       default_value: "auto",
       field_group: "rare-inherited",
     },
@@ -2476,7 +2476,7 @@
       field_template: "keyword",
       getter: "GetTextAlign",
       keywords: [
-        "left", "right", "center", "justify", "webkitLeft", "webkitRight", "webkitCenter", "start", "end",
+        "left", "right", "center", "justify", "-webkit-left", "-webkit-right", "-webkit-center", "start", "end",
       ],
     },
     {