Replace blink::WebDiscardableMemory with base::DiscardableMemory.

third_party/WebKit/public/platform/Platform.h

Index: third_party/WebKit/public/platform/Platform.h
diff --git a/third_party/WebKit/public/platform/Platform.h b/third_party/WebKit/public/platform/Platform.h
index 623c11f844c907cd1e4a3dcd080d5686e3ac2b2e..0ecf774dba8e9e6d869e836dbefa46142871f22a 100644
--- a/third_party/WebKit/public/platform/Platform.h
+++ b/third_party/WebKit/public/platform/Platform.h
@@ -70,7 +70,6 @@ class WebCompositorSupport;
 class WebCookieJar;
 class WebCrypto;
 class WebDatabaseObserver;
-class WebDiscardableMemory;
 class WebPlatformEventListener;
 class WebFallbackThemeEngine;
 class WebFileSystem;
@@ -275,13 +274,6 @@ public:
     // Return the number of of processors of the current machine.
     virtual size_t numberOfProcessors() { return 0; }
 
-    // Allocates discardable memory. May return nullptr, even if the platform supports
-    // discardable memory. If nonzero, however, then the WebDiscardableMmeory is
-    // returned in an locked state. You may use its underlying data() member
-    // directly, taking care to unlock it when you are ready to let it become
-    // discardable.
-    virtual WebDiscardableMemory* allocateAndLockDiscardableMemory(size_t bytes) { return nullptr; }
-
     static const size_t noDecodedImageByteLimit = static_cast<size_t>(-1);
 
     // Returns the maximum amount of memory a decoded image should be allowed.